The big decision will be if you should get a 802.11a, 802.11b, or 802.11g router/card standard. The most popular out there is 802.11b and these are the cheapest. They run at an optimal rate of 11mbps at the 2.4GHz frequency range. They are very cheap and the most widely used right now. The down side to the B standard is that its the slowest and the 2.4GHz frequency can get interference from such devices as 2.4GHz cordless phones and some microwaves.
However, the price is right and 802.11b seems to be the winner for me. Oftentimes you'll see deals for the router being $15 to $30 after rebates and same for the card.
Here's a couple of good links to read up on: