I see a lot of New Belgium products have already been listed but some of their must trys are; Fat Tire, Sunshine Wheat, and Abbey. The Abbey is an amazing Belgian style ale with unbelievable notes of banana esters derived from the yeast they use. If you like Hoegaarden, Abbey will more than satisfy you. If you have to have lots of hop character or bitterness, this one isn't for you.
Abbey is the beer that started New Belgian Brewing but Fat Tire is the one that took off for them. I like most all their brews except for their high dollar artsy fartsy iambics and stuff that tastes more like wine than beer.