Here is my setup:
Samsung LN52A650
P3 3 - for Blu-Ray (probably on the way out whenever OS X supports BD)
Mac Mini 2k9 ($599)

I have an HDMI cable run through the wall from my TV to the PS3 and the cable box which I'm about to ditch. I'm loath to run any more cables, so all I really need right now is something that will combine the video out and audio out into a single HDMI out and additionally an HDMI switch.

But it looks like the only decent DVI+TOSLink ->HDMI adapter is one is the Gefen which is ~$270, so I figure I might as well get a receiver for a little bit more. I'm currently looking at the Onkyos 5\606 or a comparably priced Denon or Sony receiver. Is there anything else I should consider?

I don't think receivers do the combining. Why can't you send a Toslink from the mini to the receiver and a DVI to HDMI cable from the mini to the receiver. That is how I have my iMac setup and it works great.

That actually is the plan (well I may use the mini display port -> HDMI adapter that is coming out soon.) I just need end result of my setup to be sending both audio and video over the HDMI cable going to my TV. Is that what you have setup or do you have an HDMI and audio cable coming out of your receiver as well?

I think the Gefen box is the only way to get the video and audio combined into an HDMI cable. W are running a DVI to HDMI cable to a Monoprice HDMI switcher which goes into an HDMI input on our Onkyo 706 but the audio is coming from a Toslink cable out of our G5 PowerPC. I sure do understand not wanting to run more cables. Another audio option might be a cheap Bluetooth set-up where the Mac Mini sends a Bluetooth signal to a BT audio receiver plugged into your receiver. It would be an analog input but it does work. I've done it from time to time via my MacBook Pro to the Onkyo. Of course you need to be less than 30 feet from the AVR in order to make it work. Just a thought.

Yeah, I gave up on this and ordered Samsung HT-AS720ST, since I've already pre-run some of the speaker wire this just made more sense. I figured if I had to spend ~$300 I might as well get some better speakers.