I love Sweet Frog. I originally visited a Cherryberry's, but then I found Sweet Frog. It's pretty inexpensive for what you're getting. They also have a nice plenty of sweeter yogurts, tart yogurts, and sorbets (I tend to do original tart and some mango or pomengranate sorbet). The toppings bar always looks fresh and clean, something that concerns me at some do it yourself places. Lots of fresh fruit options like Mango chunks, kiwi, and berries as well as a variety of sauces.
I particularly love these little "juice" filled poppers they have. They're kind of like Gushers but with a softer, thinner membrane. Delicious and fun to eat with the yogurt.
It's really bright and cheerful inside, too.