I know that around here X-key is all time favorite followed by G-keys on G15 and G11 keyboard, and then N52, but I still wanted to list most alternatives I know of :)
http://images10.newegg.com/NeweggIma...146-004-02.jpg
WOLF KING Warrior http://www.wolfkingusa.com/
http://images10.newegg.com/NeweggIma...169-019-01.jpg
BELKIN N52TE http://catalog.belkin.com/IWCatProdu...duct_Id=390404
http://images10.newegg.com/NeweggIma...169-003-02.JPG
Nostromo n52 http://catalog.belkin.com/IWCatProdu...duct_Id=157024
http://images10.newegg.com/NeweggIma...246-002-02.jpg
Cyber Snipa Game Pad V2 http://www.cybersnipa.com/us/product...-mouse-pad.php
http://images10.newegg.com/NeweggIma...161-023-07.jpg
Ideazon FANG Gamepad http://www.ideazon.com/us/products/fanggamepad.asp
http://images10.newegg.com/NeweggIma...175-105-02.jpg
Saitek PZ31A http://www.saitekusa.com/usa/prod/cyborgcommand.htm
http://ecx.images-amazon.com/images/...QL._AA160_.jpg
Genius ErgoMedia 500 http://www.genius-europe.com/en/prod...&ID=25&ID3=370
http://ecx.images-amazon.com/images/...SL._AA280_.jpg
Microsoft Sidewinder Strategic Commander http://www.guru3d.com/review/microso...r/index1.shtml