How about one of the "split" systems? The evaporator unit is self contained with the fans and the condensing unit sits outside much like a tradition condensor. The advantage is that you can put them just about anywhere you can run the refrigerant lines (~2" bundle) Any number of companies make them now. I've included a link but it's not a endorsement.

Of course, the cheapest option would be a thru-the-wall model.

Here is a link that might be useful: Friedrich Ductless Split Systems

A split system like mike_kaiser suggested would be my first option. Mitsubishi makes some great units, you can check them out at mrslim.com We have a bunch of Mitsu's at work and they are great systems.

Also consider adding some ceiling fans to your garage. We took an old one our of bedroom and used in over a work bench in the garage. It's among the best repurposing we've done, with something that was slightly out of style. Not only did we gain some air circulation, but we also gained three extra lights with the fan kit that came with it.

I'm having trouble with typos today!

We looked at Mitsubishi's Mr. Slim for our workshop/garage but in the end we decided to install central HVAC, which was actually cheaper. We use propane for the heat. The total system for a 34' x 34' x 10' building with 4 rooms was about $4K. Of course, we didn't buy the most efficient AC unit because we only use it as needed.