Aircraft Systems for Pilots is a good general book for GA systems...
The only problem is that it was written by Dale De Remer!
Man, his classes were a pain in the ass, but all things considered I did learn a thing or two (although it wasn't really the topic of the courses he taught). Anybody that took either Avit 411 or 407 with him knows exactly what I mean.
Wonder what the old dog is up to in his retirement...