Sam Adams isn't bad, but there's much nicer out there.
If you can get your hands on anything from Bristol Beer Factory, they do some American IPAs and a wonderful hybrid called Bitter Californian.
Probably best to buy a mixed case from an online beer seller and see what you like. Some American IPAs are wonderful, but some of them are very very strong tasting, and if you've been a lager drinker (nowt wrong with a cold bottle of lager on a sunny summer's day y'know), they might not float your boat.
Just try different stuff and prepare to sometimes taste something you might not like.
EDIT: Oh, it seems you're asking about lagers? If so, then, sorry.