Also, Ralink-based wireless cards are well supported and have open source drivers, but unfortunately have no in-kernel support (yet). In case you're interested, the link to the drivers, info, supported cards, etc is
this.
Oh, and I almost forgot, ralink-based cards (at least the rt2500 chipset which is what I'm using) work out of the box on many distros I've tried, like Ubuntu, Elive, Dreamlinux, etc. (even on FreeBSD, PC-BSD, etc.)