This is kinda a cheat, but the best solo I ever heard was actually a keyboard solo done by the old keyboard player for SAGA on their song 'Give em the Money'
It's a classic 'guitar' type solo with tons of taste and soul, plus a few runs that are almost impossible to play on guitar.
The solo ends with a duet between the keys and guitar and is probably one of the best examples of making a keyboard sound like a guitar.