There's a few choices, you can either get an IR sensor (or make one) and use any remote, or get a proper PC remote such as an ATI remote wonder (search for sapphire in uk) they cost around £30.

Personally I am using a remote wonder with girder, and it works everything I need it to, all that is required is a lot of patients to configure girder as it takes a very long time for advanced features (shift functions, mouse control etc.) anyway.

Potato