Soft cheeses usually don't have any rennet in them at all. That would be cream cheese neufchatel (probably spelled wrong), and sometimes brie and camembert (also probably spelled wrong).
Hard cheeses are fairly often made with either microbial or vegetable rennet rather than animal rennet. They are labeled as such. The ingredients list will say microbial or vegetable rennet, rather than just rennet. They're not hard to find, but aren't always labeled specifically as vegetarian cheese.
I think I heard that Kraft uses microbial rennet in their cheddar cheese, but I'm not positive, so don't quote me on that. But you don't want Kraft anyway. It's probably the worst cheese ever.
The goat cheese (chevre) in my refrigerator is also free of rennet.
Edit: It's also really easy (and satisfying) to make cheese at home, if you're interested. I would suggest easy cheeses like cream cheese, mozzarella, and neufchatel. You won't be able to make cheddar, possibly at all, but definitely not at first as the cheddaring process is long and fairly difficult at home, but colby is possible. I've made a lot of goat cheese, cream cheese, and some mozzarella. The two times I tried to make colby it rotted while aging. So soft cheeses are easier at home. And it's easy to find vegetable/microbial rennet at health food stores or sometimes homebrew stores, and you'll know EXACTLY what's in your cheese.