I am currently cycling between lifting and running, several months with either. I find that my running cycle is important because it helps to ensure my cardiovascular fitness, prepares me for more lifting, and keeps my energy levels up. The running actually help my gains in the gym. When it is time to lift, I can put the running down and really get blistered. I also take a supplement, HGH, which works good:

HGH - Human Growth Hormone Information