BTW, one correction to blamp28's tool list: Pedal wrenches are 15 mm, not 14. For many pedals an ordinary 15 mm open end wrench will work but on some models the wrench flats are too narrow and a special thin pedal wrench is required.
The absolute essentials tools that are bike specific and there are no reasonable substitutes:
Crank puller
Bottom bracket tool
Chain tool
Cassette lock ring tool or freewheel remover.
Chain whip.
Cone wrenches
Spoke wrench(s)
Pedal wrench (as above if your pedals require one)