I give my dogs Peanut butter fairly often.
In a Kong, to hide a pill, to distract while I put on their flea meds...

Or just because they love it!
(I'm so mean cuz I will sometimes put a little on their nose and watch them try to get it off. Usually they just lick it off the others nose instead! )

Also, they get yogurt and eggs and tuna juice mixed w/ their kibble on occasion, too.
Mostly just plain yogurt and eggs, though.