The first thing to acknowledge is that alcohol and high temperatures are a bad combo.
If you're not in an air-conditioned environment, it's probably best not to drink any alcohol while it's this hot. However, if you can moderate your environment a bit, a beer can definitely taste refreshing. You want to look for specific characteristics in a hot-weather beer, though. Heavy or sweet beers are out--they'll make you feel gross. High-alcohol beers will exacerbate the effects of heat and while some of them taste good, it's best to stick to something around 5% or lower. And among those beers, the best are those that are tart or dry (low in residual sugars and not sweet to the palate).
Alcohol lowers the body’s tolerance for heat and acts as a diuretic—meaning it speeds up dehydration—and affects the body’s ability to regulate its temperature. The body loses needed fluids through the urination alcohol induces....
Alcohol also raises the body’s blood pressure, increasing the risk of a heat-related illness like hyperthermia over heating and heat stroke especially for people with high blood pressure.
The good news is that a variety of styles have been developed specifically to beat the heat. The bad news?--Oregon's brewers, inhabiting a region where summers are temperate and winters are protracted and dark, aren't known for brewing a lot of them. Here's my best bet of for classic styles and the examples you can find around the Northwest:
In my humble estimation, the very best style for summer heat are the wheat beers from Southern Germany, where they're variously called hefeweizen or weisse. Although they are a typically low-alcohol beer (5% on average), they're brewed with lots of wheat, imparting a fluffy, creamy texture. They are characterized by a spicy palate that emerges from the fermentation (no real spices are added), with notes of clove, banana, vanilla, and citrus. They finish, as all hot-weather beers must, crisply; whatever sweetness you detect in the palate does not cloy. American versions of this beer tend to lack the spice (Widmer's is a case in point), though the recently-introduced Sierra Nevada Kellerweis is good. If you're in a grocery store with any kind of beer selection, you should see a German import from one of the major producers: Weihenstephaner, Schneider, Paulaner, Ayinger, Franziskaner, or Erdinger.
Across the border, Belgium produces a classic summer wheat beer much in keeping with German weisses. The word wit means "white" and indicates the cloudy, whitish color of the beer and its snowy head. Unlike their German kin, however, the Belgian variants do get their zesty, crisp character from spices. These harken back to the Dutch colonial period, when traders brought back exotic spices. Typically a Belgian wit has orange peel from the bitter Curaçao and coriander. Other spices are often added, as well (chamomile, lavender, black pepper, etc). In the US, Coor-owned Blue Moon has popularized the style, but it's a lackluster version. The original, which you can sometimes find around town is Hoegaarden. Other nice versions available in bottle are Unibroue Blanche de Chambly, Allagash. Alaskan recently introduced a year-round version that will do in a pinch.
Ah, the king of beer (styles). Considered by many to be the quintessential summer beer, and it's hard to argue strongly against them. I've written about the two main varieties of the pilsner style before (the Bohemian/Czech original and its lighter, less hoppy German brother). Pilsners are simultaneously paragons of both lagers and hoppy beers, and for some reason the former has prevented the latter from propelling this style to mass popularity among hop-loving (but ale-swilling) Northwesterners. The best examples are widely available at grocery stores--Pilsner Urquell and Czechvar on the bohemian side, Trumer Pils and Full Sail LTD 03 on the German side. Check local brewpubs, who now regularly brew a version.
The maze of tart beers is a tangled affair. They range from the merely tart to the eye-wateringly sour. Their summer-month virtues are several: a crisp acidity, lots of flavor with little alcohol, refreshing fruit without cloying sweetness. For hot-weather drinking, the best are those that aren't too tart--forget the straight lambics or Flemish reds. What you want is a light body and just a bit of zip. Full Sail still has their Berliner Weisse on tap at the Pilsner Room, and that's a perfect choice--even if you're only looking at the heat through the windows. You can try it with a little bit of syrup or straight. Upright Four, with a mild lactic zing, is perfect warm-weather beer (and word is it will be available in bottles soon). If you're feeling really adventuresome, go to a beer store and try a fruit lambic (but skip Lindemans).
Kolsch, the native beer of Cologne, can seem insipid in cool weather. In the heat they open up and refresh, with a crisp dry palate, just a touch of hopping. Hard to find good examples locally, but a delicious version inspired by the style is Double Mountain's. I love a tasty mild or bitter ale from England, and these are also very hard to find. One you sometimes see--the Horse Brass often has it on tap--is Coniston's Bluebird Bitter, a small beer nevertheless lushly hopped. Full Sail Session is tasty, but beware, at 5.1%, it's stronger than it looks. Finally, and a tip of the hat back to Angelo, the Mainer, who remembered that Sam Adams Boston Lager is flat-out one of the best hot-weather beers made in America.