Lennard Zinn, Zinn & the Art of Road Bike Maintenance, has a good discussion of what tools you need for various levels of bike maintenance. Basically, there are two types of tools: "bike specific" and "general" tools. Bike specific tools include special wrenches to deal with hubs (cone wrenches), bottom brackets and cranksets, pedals, headsets, and rear wheel gear clusters. The general tools include Allen wrenches, box and open-end wrenches, screwdrivers, and socket wrench sets. Always purchase the best quality tools of either category.