A standard set of metric and standard wrenches are like money in the bank. Get a good-quality, lightweight, chrome vanadium set. It will last a lifetime.

Adjustable wrenches threw me for a loop. To overhaul a one-piece crank, I spent US$25 on a 12" wrench in order to get the crank off...and then once it was off, I realized I needed a bigger one still to remove the fixed cone! Seriously, one-piece cranks need a ~14-15" adjustable wrench in order to turn the 1 11/16" flats. And that runs over US$50. Sheldon Brown recommends "spud wrenches" for these large tasks.

Park's plier-type CT-2 chain tool is expensive but a pleasure to use. I also like Park's cone wrenches, though if you want to economize it would be worth knowing which size you'll need.

Speaking of sizes of things, I'd say that a good vernier caliper (I got the one made by the high-end German toolmaker Wiha) may be one of the coolest tools you can get yourself. You can get far without one, but having one makes measuring much easier. And you'll spend days just measuring stuff around the house to the nearest 0.1 mm or 1/64". Which is cool.

Cool?! Well, this IS the mechanic's forum.