I am also a pretty committed bike commuter (to and from work at least) and am planning to ditch my car before moving to DC, so I will be riding a lot more. I have a Dahon Boardwalk S1 - it's the cheapest model that Dahon makes. It is a one speed folding bike, which makes it extremely portable. It does not ride nearly as well as a non-folder, but it does enable me to do things that I may not be able to otherwise, like store it at my cubicle, carry it in my trunk, and store compactly in my apartment. If you are tight on space and want something portable, I'd look into a folder. Unfortunately most of them are more expensive, but I was able to find my Boardwalk for $200 on ebay. You can get it new on Amazon for about $250.