tbonez and Mr. Sinister - halfspeed gives a good thumbnail sketch of one way to train. Joe Friel's Cyclist Training Bible is pretty much the standard reference.

Friel's books are targeted pretty much exclusively toward racers. If you don't want to race, but want to go faster and longer, one good source for training for that goal is Chris Carmichael's Time-Crunched Training Program. It assumes you have 6-8 hours/week to train, and has separate programs for racers and for other folks (like me). He does a good job of explaining the how and why of training, and of the different kinds of intervals you'll do. The training plans are much simpler than Friel's; even if you want to get into more advanced/complicated training plans, Carmichael's book makes the more complicated plans easier to understand.

A thumbnail sketch of how he does it is pretty similar to what halfspeed wrote above. You usually have two interval sessions during the week and another one on Saturday, with Sunday being an endurance-pace ride. The plan runs in a cycle of about ten weeks; you take a month or so off of structured training and do it over. It ain't easy - I kicked my own butt on this morning's interval session - but it's relatively simple. Oh, yeah, and it works, too.