I placed the order for the equipment for my MythTV backend through newegg.com. Check it out:
$156 1 ASUS Vintage-PH1 915G $103 2 HD 250GB|MAXTOR 6B250S0 SATA $128 2 TV TUNER HAUPAUGE|WINTV-PVR 250 PCI $175 1 CPU INTEL|P4 630 800M LGA775 2M R $102 1 DDRAM 1GB VDATA|128Mx64 DDR400 $895
Check out the price on those maxtors - $103 for 250G SATA. Wow.
I decided to go with the ASUS instead of individual pieces because for $156, it seemed a decent price. It had the features I wanted - one ATA and 4 SATA connectors, 4 slots for RAM (I'll get 1 board now, and can add 3 more later), two normal PCI slots and one express PCI, and 10/100/1000 LAN. Looking forward to seeing how it does.
I looked a bit at AMD systems and was awfully tempted to try them out. However, I know I need to avoid getting too exotic with stuff; I want to end up with a usable system, not a time consuming experiment. ;-)
For similar reason, I decided to go with regular, tried-and-true Hauppauge PVR-250 cards. Ted and Kees pointed out you can get cards for HDTV encoding for only a bit more ($165 compared with $128), but I think I'm going to have my hands full just trying to get multiple heads and backends NFS'd together and getting two encoders running at the same time. I'll leave the HDTV experimentation to Ted. ;-)
Note that the above system doesn't include a DVD/CD ROM. I figure I probably won't need it, but if I do, my last system came with one of each so I figure I can reuse that.