The Coors (Joe and Holly, I believe) are MAJOR backers of the ultra-conservative Heritage Foundation. In my opinion, that is a bigger problem than companies that merely donate directly to political candidates (which, they do too...$186,283 to Republicans according to Choose the Blue).
Coors Beer shouldn't be too difficult to avoid (since it taste like water) but I looked up a list of beers they brew, and I was sad to see the list included Blue Moon, which I like.
Blue Moon Pumpkin Ale
ZIMA XXX Hard Lemon Lime
ZIMA XXX Hard Black Cherry
ZIMA XXX Hard Green Apple
ZIMA XXX Hard Orange
What are some better choices? I looked on Buy Blue and I couldn't find any beers from companies that donated significantly more to the Dems than to the Republicans, but Foster's donates 53% to Dems. I'm a big fan of local microbrews. Here in Wisconsin, we have New Glarus, Great Dane, Capital Brewery, and JT Whitney's, all of which taste better than Coors (and you can get some of them in most bars and grocery stores).
If you would like to check my source about the Coors contributions to Heritage, read Blinded by the Right by David Brock.