Wireless cards are aproblematic.
Random cheap USB devices are often problematic, but no problems with real stuff like cameras. Check scanners, some are outright unwilling.
Don't get any ATI graphics card.
Super-new integrated chips on mainboard will often not work yet. Example: on my i875 I have Intel CSA Ethernet and a 5.1 card which work flawlessly out of the box. In my Athlon 64 NVidia I have NVidia's Gigabit which has some patches somewhere and some 8-channel card which has some patches somewhere else.
if you do Linux anyway, software RAID is probably the better and more flexible choice. Just remember not to use raidtoold, use mdadm (another Linux thing, elsething exists twice).