Well, actually, it wasn't all that
recently but in the past year or so.
I've had a couple of systems built around motherboards by Gigabyte: a PIII/733MHz and PIII/1GHz. Both worked well with Red Hat and SuSE. The most recent build -- an upgrade really -- used an Asus P4/3GHz. Works quite nicely. I've been pretty happy with the PIII boards with 256MB of memory. The P4 system has 512MB and runs nicely. I've used PIII systems with 128MB and had no troubles. (Heck I've got an ancient P100 with 144MB running SuSE 9.0 and other than its being slow I have no complaints. I didn't build this one; it's an old IBM desktop system that was given to me.)
I've tried to shy away from using m'boards with a lot of built-in functions (beyond the standard IDE) but that's getting harder to do nowadays. The older systems only had USB and async functions on-board. Those have always worked OK (the USB was 1.0 but it worked alright). The P4 m'board includes USB 2.0, async, sound, video, and ethernet. So far all that's worked OK but I did disable the sound and video in favor of the cards I was using before (SB512 and Abit/Nvidia Siluro GF4 MX-8X).
If the motherboard you choose doesn't have an on-board ethernet adapter, it's hard to go wrong with 3Com or Intel but they can be a bit pricey.
Nearly all of my disk storage is SCSI. Adaptec adapters seems to be the best supported. I've used some older NCR adapters for tape drives with no problems. However, the performance of the drivers for these boards when used with disk drives is spotty and seems to be getting worse. (If you're only looking at a 2.4 kernel, you might have better luck.) Somehow I rather doubt you'll want to spend the extra money on SCSI. In that case, there are a ton of IDE disks out there. I keep hearing about problems with SATA so I've stayed away from it (for now). If you plan on getting huge disks -- and it's hard not to nowadays -- you should consider find some sort of device for backups. I lean toward tape since it still makes DVDs look like floppy disks.
Cases are a personal preference; what I use you may hate, etc. Find one that has enough room for some growth and is solid enough to provide some sound dampening. The really inexpensive cases, IMHO, aren't worth it as the construction can so flimsy that the whirring disk drives and fans turns the case sides into soundboards. Watch out for boxes with small diameter fans. They have to run these at very high speeds in order to move enough air through the case and they get pretty noisy. I prefer any case that has a removable or hinged side panel. Thankfully, the case industry seems to have finally gotten the idea that clamshell covers on cases were about as easy to deal with as square wheels on a bicycle. There are a couple of built-like-a-tank Supermicro cases that I've lusted after for a long time but they're too expensive for my budget. Antec makes some nice reasonably-priced ones. So do others.
Do not skimp -- repeat do not -- on the power supply. I've had more frustrating experiences due to dicey power supplies than I care to recall.
Good luck (and make sure you account for all the screws