About.com has a **** load of information.
I plan on enlisting as well when I turn 18 (end of Nov) though I'm not sure WHEN I want to sign the line, probably not until towards the end of the school year since there really is no reason to sign when you still have time to think about what you want to do... even though I've wanted to be in the military all my life haha..
To be honest, all of the physically requirements sound pretty easy for what I'm capable of right now, but the true test comes when you have to do all of those exercises after already being tired as balls...
Anyways, I hear that today's standards are just way too easy for what they used to be.. in all branches. The DI's over the years have just been getting 'easier' and easier if you know what I mean.
edit: I also hear a lot that as long as you put forth the effort to TRY your hardest, as long as you don't suck HORRIBLY, the DI's will put you through as long as they see you are doing everything you can.
Here's all of the PFT requirements/information for the Marines. http://usmilitary.about.com/od/marines/l/blfitmale.htm