Would you recommend this firmware for my Linksys WRT54GS?

[ratchet]

It can make the routers firewall SIP-aware. I did a little reading and it seems very beneficial. The first link is the actual firmware, the second is the source for other router firmware.
http://www.dd-wrt.com/dd-wrtv3/index.php

http://howto.wired.com/wiki/Supercharge_Your_Wireless_Router_With_Open_Firmware#Find_a_Compatible_Router

[lucas1985]

Alternative firmwares are very popular. If you think that those new features are useful to you, try one of these firmwares. Before anything, make a backup of your configuration and your current firmware.

[Brian K]

ratchet,

I used this firmware and configured my old WRT54GS as a Repeater Bridge. Now I can get a signal into areas that previously were inaccessible. (eg around concrete/brick walls.)

http://dd-wrt.com/wiki/index.php/Repeater_Bridge