You could get a folding bike. There are quite a variety of folding bikes these days in a wide range of sizes and price, and they are actually pretty nice bikes. For a lot of choice (cheap to expensive, big wheel and small), check out Dahon
http://www.dahon.com/, or if you want a really high-end folding bike that folds down really small, Brompton is the way to go
http://www.brompton.co.uk/. There are a few other brands as well, like Bike Friday
http://www.bikefriday.com/.
My father commutes to work by bike, but he's moving overseas for a year, and will be living too far from the office to bike the whole way. He just bought a Brompton for just that purpose; he can ride it to the train station, fold it up, take it on the train, then unfold and ride to work.
Here's the video that really sold me on folding bikes: http://www.youtube.com/watch?v=LndpgmPLW-0