Dehydrated fruits and veggies are awesome! I love having them around since they don't go bad.
I don't have a dehydrater so I buy the ones in packages for toddlers. If I had access to a dehydrater I'd probably go crazy cutting up and dehydrating everything. Dehydrated corn is a huge hit, as well as apples. And banana. For some reason my rats didn't like the strawberries.
Also I'd try things like sweet potato, asparagus, and other stuff the rats like but I don't have around very often.
I have a dehydrator since I found it impossible to find non-fried banana chips. There's a company, I believe it's called Just Tomatoes, which sells freeze dried banana chips that aren't fried, but the price to me didn't make sense, as the dehydrator was only like twice as much.
After I got it, I did indeed go nuts. For me, pineapple was my favorite. I also have some bananas in a container that I will give to the rats whenever I normally feed them.
Though there isn't anything inherently terrible about giving your rats fried banana chips, I wanted to keep the fat down so I decided to go this route.