Any great athlete needs a few basic things: coordination, agility, strength, and power. That's basically it. Coordination and agility are always practiced within the sport but can also be practiced in the weight room by using the Olympic lifts and their variants (hands up everyone who had to do cleans as part fo your highschool football program). Here are a few links that might be helpful.
Westside Barbell and football training - Westside Barbell is the most notorious gym in the world. It produces more powerlifting wonders than any other. This article deals with applying their methods to football. (It is also written by a man who should know about these things...)
Extra session for football players - by the same writer as above, it details some 'extra' workouts that might be beneficial for the aspiring football player.
Renegade strength training for football - Some of the exercises here are slightly unconventional but coach Davies tends to know what he's talking about and he makes some good points. Fairly good explanations and illustrations of some olympic lift variants.
The 'next big three' - This program expands on Bill Starr's original "Big Three" program (also covered in the article) that has the been the staple of many a football program through the years. It is mainly directed at in-season training but well worth the read.
General guidelines - This little article (don't expect much) is short and sweet. It does deal with some very good points though and it's probably the first thing you should read about getting in shape for football.
That's a good start. You can always continue by doing a more thorough searh on the net (and logging on to the Renegade Training website is always a good idea).
Oh, and you might want to check this out for .
all-around advice for youngsters in sports which talks mostly about what
not to do.