If you really want to get into it seriously, you'll need truss rod tools, nut files, a good straight edge, a six inch ruler (you could use either system, but it is probably better to to use whatever your books are using), a variety of screw drivers, nut drivers, basic electronic stuff (which you probably already have, if you are on this board), and a string winder and cutter. If you want to be a little more involved, you'll have to get a strobe tuner (nothing else will do for setting intonation - nothing). If you want to do fret work you'll need a good brass hammer, small and large end nippers that have been ground flush, a big flat file for leveling frets, and some kind of file for re-crowning them (I don't much care for "fret files," and much prefer an 8" bastard file with the edges ground safe; it works faster and is more versatile, but it does take considerably more skill to use), and something for truing fingerboards (this can be as simple as a 24" level, or more complicated such as one of Stew-Mac's
aluminum sanding beams. More advanced repair work involves some pretty specialized wood working tools (deep throat clamps, jacks for gluing braces and the like, heating pads, etc.), as well as some more basic ones (chisels, files, a drill press, band saw, belt/disc sander, some way to sharpen your chisels). There's a whole bunch of other stuff, but you'll never really know what you need until you need it.
Gabriel