Taken directly from the Tomato web page:
What will this run on?
* Linksys WRT54G v1-v4, WRT54GS v1-v4, WRT54GL v1.x, WRTSL54GS (no USB support)
* Buffalo WHR-G54S, WHR-HP-G54, WZR-G54, WBR2-G54
* Asus WL500G Premium (no USB support)
* Untested but apparently works without changes: SparkLAN WX-6615GT
Note: Most WRT54G and WRT54GS (not WRT54GL) sold in stores right now are the v5.0+ variety and will not work with Tomato.
http://www.polarcloud.com/tomato
EDIT:
Just buy this one, it's the best you're going to find:
http://www.newegg.com/Product/Produc...82E16833124190