Racing wheel 360/PC

This may belong in hardware, so I'll post it there as well.

 Can anyone suggest a good racing wheel that would work for both the Xbox360 AND PC (if such a creature exists).  If it worked for PS2/3, even better.

Does a racing wheel add much to the experience of a racing sim?  I think it would if the whell/peddles were done right, but I've never used one. 

Thanks