Yep, can't go wrong with a decent vintage bike that suits your needs gotten at fair price or better. Later, if you determine you need something a little different, you can upgrade/modify it, or get all your money out and maybe more by re-selling it. Take a look at the C&V (classic & vintage) forum here http://www.bikeforums.net/forumdispl...lassic-Vintage ; lots of know how to be gleaned about choosing and caring for a vintage bike.
Along with mountain bikes, you should consider touring and "sport-touring" road bikes; they are emminently suited for on-road commuting: fast & light, comfortable, and typically have attachment points for fenders and racks (as compared to more single purpose road quasi-racing bikes). The more serious touring models will have cantilever brakes, a real plus for a laden bike and/or in wet conditions.