Sweex LB000021 / Edimax BR-6104K Router
 

Also the same, Dynamode 6004 and maybe a few others.

Just got this (not installed yet) really only as a belt and braces for the software firewall.

Interesting site:
http://www.norocketscience.com/router/upgrade.htm

The latest official firmware is 2.97 (with Linux source) from Edimax
(some of the discussion/hacking predates the GPL opensourcing)
For the Sweex model, their firmware for the LB000021 is BR-6104k 3.01

Projects include:
1. Migrating to a Linux 2.6 kernel
2. hardware hack, serial console
3. hardware hack, USB port - software support still under development, but the happy hackers aim to have USBdrive server support - though the router won't fit back in the case