I've got a Keysonic wireless keyboard with usb wireless dongle, also has a built in trackpad, making it ideal for web surfing etc.
I've got this Keysonic KB from ocuk of course , out of stock but should get more soon. Works with the PS3 perfectley, really good value 2 !
http://www.overclockers.co.uk/showproduct.php?prodid=KB-001-KE
Is there a key you can press on the keysonic to bring up the XMB? Pressing the Windows key whilst on the XMB puts you back in game but doesnt work the other way around?