WRT54Gs have several pages that aren't linked by default. I have posted them below. Some of them provide useful information. This pages are only for the WRT54G/GS.

Pages and content may vary with different firmware.

SysInfo - Provides general information such as MACs and revision information.
Site Survey - Searches for other nearby access points (N/A on Linksys firmware)
Wireless Active Table - Displays active wireless clients
Cysaja - Provides non-humana readable information on router.
SysInfo1 - Provides mainly hardware information