You can dehydrate absolutely anything, if you do it right! What sort of dehydrator is it? Some have setting for yogurt-making too.
But seriously, people dry everything, fruits, veggies, meats, nuts, grains, eggs, milk, soup... I've done fruits and veggies, (leather is especially good) some things can be air-dried but will dry quicker in the dehydrator, like herbs and some green beans.
The specs on the different foods are different. Some you want to dry at a high heat, while others will scorch. Do plenty of research! And bear in mind, drying things like meat, eggs and milk can be dangerous if messed up, so keep an eye on them.
Here are my favorites:
Dried celery (It's surprisingly good... Naturally salty-tasting)
Beef Jerky (I've lived for days on the stuff while camping)
Leather/fruits (Sweet, healthy snack! Peaches and asian pears do very well!)