The good and the bad.
 Belgian Beers
Try one of the Belgian offers that are usually available at Cole avenue and Spring Street:
Hoegaarden Witbier (the King of white beers) 5%alc.
Blanche de Bruges (white beer, which you are obviously supposed to have in a grail. awesome)
Duvel (golden ale, absolutely amazing, clean, balanced, crisp and oh so good, the King of Belgian Beer, period. This is what people in Bruxelles drink) 8.5%ABV. (Purple Pub now has 'Duvel Green' on tap which is the same brew but it doesn't go through the second fermenting in bottle, resulting in different flavors and a lower abv 6.8%)
Grimbergen (pretty darn sweet! abbey ale)
Lindeman's Lambic ale (flavored with cherries, peaches, etc...it's a highly unique beverage)
Stella Artois (import that thinks it's a domestic beer, not commonly found in Belgium as the locals know better)
Commentary on the above: Hoegaarden > Blanche de Bruges. Duvel and Grimbergen are tasty. Lindeman's tastes very different from normal beers, but there is no essential difference in the method of brewing. For a nice selection of Belgians, try the Beverage Den on Rt. 7 in Bennington. They've got Orval, Chimay, Rochefort, Witkap Pater, Cantillon Gueuze, Saison Dupont, de Ranke xx Bitter, and some other stuff. However, they do not have Brugse Straffe Hendrik, which is unfortunate. For cheaper belgian style beers, Allagash, Unibroue, and Ommegang are all awesome.
 Other Imported Beers
If you hate the Belgians (and, after all, who doesn't?), here are some other great imported brews:
Samuel Smith - Oatmeal Stout, Imperial Stout, Taddy Porter, Pale Ale, Nut Brown Ale, and Winter Welcome Ale. (UK)
Unibroue - Le Fin du Monde, Trois Pistoles, U2, Ephemere, Terrible and others (Canada)
Celebrator Doppelbock (Germany)
Spaten - Optimator Doppelbock, Oktoberfest, Pils, and Premium Lager (Germany)
Newcastle Ale (UK) - One of my favorite brown ales. For those who like a slightly sweet beer with a just-bitter-enough aftertaste. Yum.
Guinness Brewers (Dublin) - Guinness (Irish stout), Harp (Lager), Smithwicks (ale) are all excellent. If you like a black and tan, Gunness and Harp is where it all started.
Sol (Mexico) - A mild, agreeable blonde.
Pilsner Urquell (Czech Republic) - The one that started it all. The original pilsner. What more is there to say?
 Domestic Beers
 Craftbrewed/Microbrewed Beers
Speaking of local beer, the residents of Currier S suite '10-'11 are known for their mad brewing skillz. Ask one of them for a sample! (moved to microbrew section, their fine product is definitely a craft)
Stone Imperial Stout
Sierra Nevada One of the largest CraftBrewers in the country. They have managed to grow to a national distribution without sacrificing quality. Their Pale Ale is a beer you will not regret trying.
Sam Adams Boston Lager Another large Craftbrewer. Their Boston Lager is quite nice. The Summer Ale is quite possibly one of the more perfect beers on a hot summer afternoon.
Otter Creek is absolutely fantastic. The Vermont Lager is one of their "year-round" beers, and it's probably the smoothest tasting of the bunch. If you're looking for a little more kick, the Pale Ale (also a year-round) is one of the best I've ever had. For even more of a bitter aftertaste, try the seasonal Alpine Ale and the Extra Special Bitter (I don't particularly love them, but you might). Another interesting seasonal is their Middlebury Ale, which is chock-full of blueberry taste. It's a bit overwhelming at first, but it's worth picking up a six-pack to try it out. Their Stovepipe Porter is dark, smoky, and delicious.
BBC brews up some mean beers. Almost anything by them is great, though the Steel Rail Extra Pale Ale is debatable. Support local beer! The BBC Imperial Stout is easily one of the best Imperial stouts you can get anywhere.
Tröegs Brewing Co. from PA brews a wonderful American Pale Ale.
The Long Trail Ale Brewing Co. (near Killington, VT) brews some great beers, the Double Bag (dusseldorf altbier 6.7%) is excellent.
Honey Brown is another great beer; brewed in Rochester, NY, it goes down smoothly but still has a great taste. Great as a casual beer, or with a meal. Relatively inexpensive, too...about as much as Coors Light, but so much better.
 Macrobrewed Beers
Milwaukee's Best, aka "The Beast." A great first beer to try and a Williams favorite. Excellent, full flavor, it's a real beer experience yet light enough to play Beirut or Flipcup with. Very well priced for such a great beer. It's especially enjoyable if you burn off your taste buds on any given night.
Not sure what the previous person meant by the words "excellent" and "full flavor." Beast is generally acknowledged to be the cheapest beer available, and hence, it is immensley popular with college students. In addition, it goes down smoothly, and is great for froshies still "finding their way" in the drinking world. Beer is an aquired taste...this is why adults routinely enjoy beers with meals and at parties, whereas younger people typically "drink to get drunk." Given this fact, many college students (especially girls) find beer hard to drink initially. Beast (light, of course) solves this problem by diluting the taste while still allowing kids to get drunk. Overall, a great beer for large parties given its inexpensiveness and easyness to drink factor.
Rolling Rock - Perhaps not deserving of the "good beer" title, but it's one of the most drinkable cheaper beers out there. A 30-pack will set you back about 20 bucks, and it isn't half terrible. (also light enough for Beirut or similar games)
Yuengling is a good macrobrew, though hard to find in the Northeast.
Genny Light: Perhaps a slight mix between gasoline and sink water, this is simply not worth the intoxication. Your tongue will thank you if you just chugged rubbing alcohol instead. This is also a mainstay at Lehman Hall...so bring your own beer- unless you ask for different.
 Bad beer
One easy way to judge whether a beer is bad or not is by the color of its can. the so called "silver and blues" are generally the bad beers. ie beast, natty, busch etc... This 'judging a book by its cover' works every time. Also, in case you hadn't noticed, not many good beers come in cans.
Don't be fooled into believing a beer is necessarily good if it is imported. Some of the overpriced, well-marketed "Euro" beers (e.g. Heineken or Stella Artois) can be just as bad as the American macros.