1) I have a USR v.Everything 56K for ~$25 but it's ISA. I can't remember if the ASUS board has an ISA slot--if you want it let me know. A PCI USR is going to cost you ~50-100 but it's worth it.
2) I have the ABIT NF-7s. It kicks ass (but doesn't have an ISA slot).
3) If you decide to go AMD you can pick up a 2100+ for half of what you are going to spend. It's a monster and, last I heard, the best overclocker. Mine's clocked at ~3 GHz right now (~$200 savings =) ). Make sure you read up on the right boards to find out which one to buy. I got mine from newegg but I don't know if they are still guaranteeing delivery of the chip I have.
edit:
4) The Sony CRX220A1 is a rebadged lite-on. All you need to do is flash it with the lite-on firmware (grab it from
http://kickme.to/sony195) and the turbo button is always enabled, the lights work (red when burning instead of green), and Mt. Rainier support. It kicks ass, too.
Review and $20 dollar rebate