The Linksys WRT54G is great because you can replace the firmware (based on Linux) in order to tweak the settings to your liking (like restricting wireless access based on MAC addresses). Just make sure that you get a version 4 (serial number begins with CDFA...) in order to change firmware.
http://en.wikipedia.org/wiki/WRT54G
I have a WRT54G and a WRT54GS that I bridge (both are running dd-wrt firmware) in order to connect my XBOX wirelessly (the XBOX wireless adapter was $150can, and I paid only $80can for the WRT54GS). Runs great and serves as an access point for other PCs at the other end of the house
