What is the best portable air compressor for my nail gun?

How big of a portable air compressor do I need to buy to run a nail gun? I am rebuilding my garage and a want to use a nail gun on the project. I have an old compressor that recently quit on me and I am looking for a replacement.

When looking for a portable model for nail guns there are basically 2 types most people use. There is a pancake tank style and the twin tank model. Air nail guns typically do not require too much air to run, so you can get by with a smaller tank. In this case a pancake tank model is great because they are small and easy to haul around. The twin tank models are typically bigger and have wheel barrow type wheel in the middle to tow around. If all you are running is a nail gun for a home improvement project, I would go with a pancake type portable air compressor.