Astoria has several great places to buy beer, especially in north near Ditmars. Check out the Euro Market on 31st Street between 30th Avenue and 30th Drive. Not only does it have a 40+ foot freezer case of bottles, it also has some great smoked meats and imported groceries.
There's also Best Yet Markets, at 37th St., just north of 20th Ave. They have a great beer selection, as do most of the grocery stores in the area--there used to be a big Czech population around there.
There are also a lot of bars in the area with great taps. One of my favorites is Sunswick, at 35th St. and 35 Ave. The staff are really friendly and knowledgeable about the beers on tap. They're usually happy to let you try a few samples.