I can't believe that this router hasn't been discussed yet here. It looks like the sky is the limit with this little piece of hardware.
Here are just a few of the things that they have running or found on this router:
USB
Serial
PCMCIA?
VPN (Server/Client & Pass through)
Bandwidth Management
SSH
Client/Bridge mode (WiFi)
The only limit is the flash right now. I think I'm going to go out and buy one today.
RAM: 2 x IC42S16400?, 64Mbit (4M X 16) RAM chips (16MB)
Flash: AMD AM29LV320DB-90EI, a 32Mbit chip (4MB)
CPU: Broadcom BCM4702KPB, with a 125MHz MIPS and two 10/100 Ethernet controllers
Ethernet: ADMtek ADM6996 5 port 10/100 switch
Wireless: Mini PCI slot with Linksys/Broadcom radio FCC ID PKW-WM54G, dual Hirose antenna connectors (1.0 only - version 1.1 hardware has the wireless integrated with the mainboard)
Ports:
WAN: One 10/100 RJ-45 port for WAN connectivity
LAN: Four 10/100 RJ-45 Auto-MDI(X) switched ports
WLAN: 54mbps 802.11g on a MiniPCI card (1.0)/built-in (1.1) with dual external RP-TNC antenna ports
LED Indicators (1.0):
Power, DMZ, Diag
WLAN: Act, Link
LAN: Link/Act, Full/Col, 100
Internet: Link/Act, Full/Col, 100
Channels: 1-11 (USA)
A detailed breakdown of the hardware/software:
http://www.seattlewireless.net/index.cgi/LinksysWrt54g
Current forum on hacking it with builds available:
http://www.sveasoft.com/forums.html
Possibly an unused PCMCIA/CF slot:
http://www.sveasoft.com/postt203.html