intervel training
This is one of the better articles I've seen on it because it has a few pictures and simplies it for gym training.
http://www.t-nation.com/readArticle.do;jsessionid=5E2DE4AFFD 0A8D3E50C74138E1128CDA.hydra?id=1756065
There's some guys over on the Men's Forum that love it. It's basically a lot of hard work. Check out some of the video workouts on this site too.
http://www.crossfit.com/