One tool we've learned we can't live without is an air-powered paint sprayer. This month alone we have painted up two huge work tables, a large dining table, two small tables, a chair, a chest of drawers and several frames. I should say, Isaac has painted up all of these things. I just ran the kids around and made all of the dinners so he could keep at it. For three weeks, our front driveway housed what looked like a terrorist interrogation tent, dusty tarps flapping in the wind. Isaac called it his "hobo shanty town." Painting this many pieces would have been misery with a paint brush and the finishes wouldn't have been so smooth and professional.
Of course, it would have taken far less time if we weren't experimenting with some bullet-proof, professional paint Isaac tracked down. This stuff was rough to use, but the finished work tables are hard as glass. We used regular paint from the hardware store for all of the other projects and they were far easier to complete.
We have refinished a ton of furniture over the last 15 years. I regret not getting an air compressor and a paint sprayer sooner.
As far as air compressors go, for spraying paint, it's important to get a compressor that is large enough and powerful enough to keep up with you. Usually you would need, at minimum, a 20- to 30-gallon compressor for powering a paint sprayer because you are using the compressed air in a steady stream instead of in short bursts (as for a nail gun or staple gun). However, we have found that the 15-gallon DeWalt D55168 is up to the task. It has an extra-powerful motor and is capable of being filled to a very high pressure -- many 30-gallon compressors will only go up to 140 PSI (pounds per square inch), while this guy will go up to 200 PSI so it releases a longer flow of air than you would normally expect from a smaller tank. And it takes up less room. Furthermore, when we turned this machine on at the store, we found that it was also considerably more quiet than other models. Sold!
Make sure to compare the SCFM ratings (Standard Cubic Feet per Minute) of the compressors you are considering, which measures air flow (into the tank, I think). For spraying paint, you will want a machine with an SCFM of 5 or more. Most air compressor tools will list what SCFM is needed to operate them, so look at the different tools you will want to use before choosing which model of air compressor to purchase. If you plan to use an air compressor for tasks that only require small bursts of air, like for a nail gun or a staple gun, then you might be able to get away with a smaller compressor. Read more about how to choose an air compressor here.
In my opinion, the gravity-fed pneumatic paint sprayers (with the paint tank on top) work a little better than the siphon-fed ones. I haven't used enough different models to say which brand/model is best. Ours is a Husky Pro HVLP and we have been plenty happy with it thus far. Make sure to get a professional-quality respirator to wear while you're working.