There are so many options, it's hard to believe everyone doesn't know about HDTV.
I suggest starting out by thinking about what exactly it is you want. The only obvious thing is the digital decoder. Since you have Directv, the DTC-100 is the best bang for your buck although you'll probably need to get another dish to get the HD channel(s).
Since the DTC-100 upconverts 720p to 1080i, no need for a monitor that does 720p natively. A 4:3 is a lot cheaper than a 16:9 and you don't need to sit as close to get full enjoyment out of the picture. (Direct view 16:9 sets generally require you to sit 4-5 feet away from the set to get HD in all it's glory. 4:3 sets generally don't have the resolution so you can sit a more "normal" distance from the set, say 8-10 feet away.) Keep in mind the 16:9 sets, overall, have much better definition.
If you plan on a lot of DVD's, then a 16:9 set may be worth the extra cost. You may decide to spend an extra $200 for a progressive scan DVD player.
Do you need a line doubler for NTSC signals? Some sets have decent ones but others are poor. It may be worth getting a line doubler even for Directv. That's an addional $5-600, though.
Once you decide what you need, check out TWICE.COM as they have a really nice list of almost all HD sets and monitors available along with their retail price. (Some monitors don't have tuners so you may need to use a VCR as your tuner.)
Since all these sets are very heavy, you may want to consider reinforcing the area the set will be placed in the entertainment center.
You could get a nice 4:3 system for around $2300 and a solid 16:9 sytem for around $4300.