Best short-range wireless router signal booster

I have a Linksys WRT54G that gives a decent signal in a multi-floor home, but it does fade out in various rooms due to distance from the router. To boost the signal, I understand that there are several options, such as a powered external antenna or a repeater.

Given the headaches of finding a good repeater and getting it to work properly with various security standards, I'd rather go with a supplementary antenna. All I need is an extra 30 feet.

Any recommendations on an antenna booster for this purpose that will work with the WRT54G?