Local places are almost always best - if you find a roadside market or fruit stand that sells ice cream, you can bet it will be good (especially in the fresh waffle cones they'll make right in front of you) - but for chains, Ben & Jerry's has a lot of creative flavors, Baskin Robbins just has a good variety at a good price, and Cold Stone Creamery is a bit pricey but a lot of fun. At Cold Stone you start with a basic ice cream flavor- they have like 10 - and then add "mix-ins", like brownie chunks or nuts or sauces - stuff that would normally be toppings. They literally fold it into the ice cream and mix it on, well, a cold stone.

>>14 seems to imply that Haagen-Dasz has a chain - never seen one of their stores, but their ice cream is the best of the store-bought, at least for normal flavors. Again, B&J has the bizarre flavors.