All of the yeast manufacturer's list the optimum temperatures of each strain on their website.
Some strains are fine at 57-59 degrees, while others need to be a bit warmer. I've made lager-like beers with pacman at 60, nottingham at 59, and alts and kolschs in the high 50s.
Remember that it's the actual fermentation temperature that's important- not room temperature. In a warm room in the the summer, I've seen the fermenting beer be 10 degrees warmer than ambient! Usually, a cool ferment will only be a degree or two warmer, sometimes three, than the ambient. If you get a stick-on thermometer for the fermenter, that's pretty close to fermentation temperature.
I have a cooler that I use to keep my ales cool enough in the summer. I put the fermenter in a water bath, and cycle frozen water bottles in it to keep the desired temperature. I do sort of the same thing in the winter, but this time it's with an aquarium heater in the water bath. It was cheap (under $10) and I can keep my fermenting beer at 70 degrees if I want, with that aquarium heater in the water bath. (There are pictures in my gallery if you want to wade through 100 other pictures first!).
Broken Leg Brewery
Giving beer a leg to stand on since 2006