OK Mike, sorry for the delay, but here's some ideas for you...
For a hot summer day, I don't think that a nice wheat beer can be beat. There's lots of good ones to choose from, both domestic and imports. There's a number of styles within the wheat beer category. Belgian style, Berlin style, Hefewizen, Dark Wheat (Dunkel Weizen). Belgian style includes some of my favorites including Celis. This style uses Curacao orange peel and coriander in addition to the barley malt, hops, water and yeast. Another good one is Blue Moon which is made by Coors. Germany produces lots of good examples including a very sour beer, called Berliner Weisse, which is the Berlin style. First time I had it, I HATED it. A few years ago, I thought I should give it another try, and this time I could appreciate its qualities. Hefeweizen's are also very good. Hefe means yeast, so these beers have a small amount of yeast remaining in the bottle. Schneider Weisse is the most commonly available example. Franziskaner Dunkel Hefe-Weissbier is an example of the dark wheat style, which also has yeast in the bottle. I'd say that all of these could fit the bill for your summer BBQ, but I'd also add Pale Ale and English Bitters. The classic PA is made by Sierra Nevada, but there's lots of good ones to try. Bitters would be noted by ESB (Extra Special Bitter) on the label.
Now for the tailgate football party, just about anything goes, depending on what you like, but my cooler would be nicely stocked with India Pale Ales, cuz hops make me hoppy
Once again, there's a huge number of IPA examples including Hop Devil, Hop Pocket Ale, Grant's IPA, Magic Hat IPA. You just gotta try 'em all!
Especially if you're at a football game with a bunch of good friends, enjoying some good food before & after gametime.
For that cold winter night, you gotta crank up the alcohol content a bit to warm yourself up, so you want a nice Imperial Stout (Samuel Smith's Imperial Stout or Grants IS) or a Barley Wine. Amongst Barley Wines, I'd suggest Thomas Hardy's, Sierra Nevada's Bigfoot Ale, Brooklyn Brewery's Monster Ale. Old Ales can be nice as well including Young's Winter Warmer or Old Peculier. Another style is Bock beer with Aass Bock as one of my favorites; also Celebrator's Double Bock, which is very good.
For that dreary rainy spring day, you should go for a Maibock. Try Rogue's Maierbock Ale.
For that steak dinner at your local restaurant...don't ruin it with a Bud or a Miller. Get yourself a nice glass of BOURBON!
Hope this helps you find an appropriate beer for the situation!