A British mild is always a good bet for a quick beer. I had mine fermented, kegged, and carbed up for drinking in less than 10 days. (See this thread: http://www.homebrewtalk.com/f38/proj...th-10-a-77758/)
I don't like wheat beers, but a hefeweizen would be quick and easy, too.
The keys for a "fast" beer are a fairly low OG, no complex roasty flavors that need to mellow and meld, not tons of bitterness, and something that you don't care if it's clear or not.