I have a HD DVR from Directv (HR20-700) that I use with a Panasonic DVD recorder to record from the DVR HD to the DVD recorder. The Panny model I use only supports single layer DVD's and I think I could a lot better quality recordings with DL. Can anyone recommend a quality DL DVD recorder for this use? I'd like to hear from anyone who has any experience doing what I'm proposing to do? TIA!

Probably the biggest factor in your picture quality would be if your STB outputs WS over S-video, hopefully yours does, if not I'd look into a component to S-video converter for the biggest picture quality improvement.
You didn't say which Panny you had, but from '05 and beyond Panasonics have recorded full resolution up to 4hrs/standard DVD, with <3hrs being better for faster motion scenes. That being said anything closer to SP or 2hrs/SL disc is best for reduced macroblocking. If you have a '04 and older Panny just updating to a newer unit should give you better >SP recordings.
All Pannys from '06 and on have recorded to DL media. The most current Pannys, the x8 series can record continuously from one later to the next. In your case I'd look for a Panasonic EA-18 (http://www.avsforum.com/avs-vb/showthread.php?t=1021745&highlight=panasonic) which is tunerless and provides the easiest DL recording.
Personally I rarely use DL discs because I rarely record things over 3hrs/disc but with a Panasonic it's nice to have the option to use the DL discs.

Keep in mind that DL media is ridiculously more expensive than single layer, its long-term durability is open to question, and there is only one brand of DL media guaranteed to work in every recorder (Verbatim +DL). Overall DL media has been a big fat disappointment and is not the holy grail everyone was hoping for. For occasional use its OK, but for permanent library recordings you're better off with SL media. Using SP speed on SL discs is about as good as it gets, you can squeeze longer movies up to 2.5 hours on a disc using the flex record speed feature on Panasonics or the 2.5 hour "speed" of other recorders. Very long movies should usually just be split across two SL discs. jjeffs tip regarding the widescreen setting on your PVR is true: you'll get more of a quality improvement by making sure the letterbox feature is turned off.

While I don't actually have an HR20-700, I have had four different DirecTV DVRs and all of them put out a full screen horizontally compressed (anamorphic) picture out the S-Video connections when widescreen content is played back--ID the settings are correct. I have no reason to think that the HR20-700 would be different. This would be the best method, and it's what I use.

As has been said, DL media is very pricy compared with single layer media. If you insist on using it, I have to agree, my use of Verbatim +R DL disks has been very positive. All of my recorders have intgernal hard drives, so I don't do realtime recordings, but jjeff has said that you can record continuously in realtime, and he is rarely wrong about these things.

You said you wanted better quality, so what quality setting are you using for your recordings? What model of Panasonic are you using?

The only way you will get a better quality recording is if you take advantage of the greater capacity to increase quality selection for recording (SP for LP, or EP for SP). Bear in mind though that DL disks are not twice the storage of SL disks, so if you do this, you will actually have less time than on an SL disk. What I mean is, a DL at XP is less time than an SL at SP (the next quality setting down).

I'm using a Panasonic DMR E30 and always use the SP setting with SL DVD's unless the duration of the recording is over 2 hours and then I use the Variable option. This recorder doesn't support DL.

I was hoping that using a Panasonic recorder that supports DL I could use the XP setting for a 2 hour program or use the Variable option for greater than 2 hours and get a better quality recording. I was thinking that the recorder would use lesser compression when recording with DL rather than SL.
Any ideas?

Sure, you can use DL discs on a DL recorder to fit about two hours of XP on one disc. Will it give you a stupendous improvement over SP on SL discs? No. Depending on the quality of your STB signal, it may barely be noticeable. Is it worth spending $1.35 per DL disc for the slight improvement? Only you can decide by trying it: I'd recommend asking around if anyone you know has a DL recorder you can borrow before spending the money on a new one. New recorders are not necessarily better than old ones, most are in fact worse: you'd basically only be getting the DL feature added to the same machine you already own. Also there truly is a limit to just how much performance you can squeeze out of standard-def DVD recorders: they just don't cut it with the nasty pissy large LCD displays we use today, which practically require live hi-def input to avoid looking like hell. They don't like SD burned DVDs at all, no way around it: you'll never achieve paradise.

Remember to factor in future playability and compatibility: DL media is inherently flakey and weird, even the Verbatim (which is the only DL brand worth spending money on). Many DVD players have trouble reading burned DL discs, and a surprising number are not that thrilled with XP either. There is a gamble involved using DL media and that gamble is compounded by using XP speed on it. It really depends on how serious you are about your library: if your approach to it is casual, and you're not the type to lose your sh*t when something goes wrong later, then sure play around with DL/XP. But if you're very into your video collection, you may not want to mess with "extreme burning". The number one reason most people buy DL media is to make computer-burned backups of commercial DVDs they own, for the kids to handle or for travel/portable use. For such transient "convenience" uses DL comes in handy.

The E30 is one of the first Pannys and according to this chart (http://www.avsforum.com/avs-vb/showpost.php?p=16171983&postcount=1)it's a '02 model year. Since it's before '05 it will drop resolution to 1/2 D1 on any speed above 2hrs/disc. I'm not positive about FR above SP speeds but if it's similar to '05 and newer machines which drop resolution after LP, even a 2:01 minute FR recording might drop to 1/2 D1, similar to '05 and beyond where 4:01 in FR will drop to 1/2 D1.
If I haven't confused you with the D1 talk suffice it to say with a newer Panny such as the EA-18 you'll be able to record more than 2hrs to a disc and still keep full resolution. With that in mind unless your recordings are much over 3hrs long, you may not need to use DL discs after all, but with the EA-18 you've got that option.

jjeff is right, I didn't realize you had such an old Panasonic:o: if you can afford it, you'll definitely see some overall improvement with a newer Panasonic like the EA-18 (the very early Panasonics had some bugs and PQ issues). In your specific case, assuming you stay with Panasonic, a newer model will outperform your old one even using ordinary SL discs and the SP speed. This might be enough of an improvement for you not to bother about a "dual-layer and XP" experiment, although the option will of course be there on a newer Panasonic. My earlier opinion on DL/XP still holds;).

The Panasonic EA-18 is the perfect accessory for a cable/satellite PVR and often recommended here. It can be difficult to find but its worth the search. An alternative would be the EA-38 which is the same recorder with a VHS deck added. If you get really stuck, and can't find either of these tunerless models, you could opt for the EZ-28 or EZ-48 which include the tuner. New Panasonics with tuners have a lot of issues, mostly related to their tuner/timers being unreliable, but if you're only going to use it to back up your PVR recordings you likely won't be affected by those issues. The advantage of the EZ-28 and EZ-48 is they're easier to find and often good deals are offered on factory-repacked units. Check web dealers like uBid.

I'll second... (third?) what jjeff and Citibear said. DVDRs are dying out. Get a new Panny while you can. Burn the same thing in XP and SP to good quality discs, Verbs, Tayio Yuden... watch them on your system, and see if you can tell the difference. You might want to look at them with your TV zoomed, like to fill the screen with a LB picture. Is there enough of a difference to use DLs at XP? Your equipment and you are the real determiners of the answer.

I have a 56" 720p DLP. I sit about 8' away. I have a Pio 640 DVDR with HDD. SD sources recorded at SP are virtually identical to the original source, to my eyes. When I zoom for LB films, I can notice some slight difference between SP and XP.

My practice is to record up to about 130 - 140 min. programs in SP, especially if they are in B&W, and or don't need to be zoomed. Anything else, I either split at a break in scenes, between two SLs, (made easy by having a HDD) or I use Verb +R DLs. I've probably burned close to 100 DLs, and never had a coaster.

I was hoping that using a Panasonic recorder that supports DL I could use the XP setting for a 2 hour program or use the Variable option for greater than 2 hours and get a better quality recording. I was thinking that the recorder would use lesser compression when recording with DL rather than SL.
Any ideas?
This will indeed work, and there certainly will be less compression putting the same program on a DL in XP verses an SL in SP quality. The question is, will that actually give you a noticeably improved result. Unless you have really great eyesight, and a very good television, it is unlikely that the improvement will be even noticeable. Wiith DL disks being at least 4 times the cost of SL disks, and the uncertainty of their burn quality and stability, it seems like a questionable direction to take. I have had difficulty using the flexable record option with DL disks. Unless panasonic has really improved that function, I would not count on using that. My newest recorder is an EH55 though, so they might have done come work in this area.