“Linksysinfo”:http://www.linksysinfo.org/portal/forums/forumdisplay.php seems to be the place where all the various firmware projects are discussed.
I’ve used DD-WRT and it worked OK, but when I upgraded our WRT54G to HyperWRT Beta 21, it completely bricked it, so beware.
Other projects I haven’t tried include Svearsoft, EWRT, HyperWAP. Also there is the MustDie Firmware for WAP54Gs.
Another thing is that “Linksysinfo”:http://www.linksysinfo.org/portal/forums/showthread.php?t=42554 has a post for a fix for v3 WAP54 that lets you set the power up to 100dbm so past the FCC limit, but you get more power. Of course you also need more power at your clients too.