The first time you wake up to a flat tire and are able to fill it up with your air compressor instead of changing it, the price of a decent size compressor becomes easily justified, IMO.
I bought mine (and a nailer) when I fenced in my backyard. The money I saved putting up the fence myself easily paid for the compressor, extra hose, nailer, and other tools.
I have used it to rescue my neighbors on either side when they had flats. We have a tire shop less than a mile away so unless the tire is slashed, we can fill it up and drive it to the shop before the tire goes flat again.
I also have used it to blast debris out the cracks in the driveway and walks before caulking, to pump up an inflatable couch/hide-a-bed, and blast the water out of the gears and chain of my bike after washing it. Plus cleaning all sorts of electronics.
I do recommend an upright model - similar to this one for a few reasons. They have a smaller footprint than horizontal models - nice if have a small or crowded garage. I find them easier to move around too (if you don't have 500 feet of hose to reach the neighbors). Also, the outlet is much higher, above any pooled water, and less likely to be spewed out (or clog up the filter).
