Your diet is half of making your goals in lifting, whether it's to bulk up or lean out. I bike, play racquetball and lift 5x a week and have kept a combination of this routine up for over 14 years; lifting has been a fair portion of my excercise because it's something I can do year-round.
I'm creeping up on 30 and my goals have switched from bulking up to staying lean and strong, although I'm all of 155 lbs at 5'11". Through it all, staying away from carbonated drinks as much as possible and eating well has been most of the battle. I played with Creatine for a spell and I'll not deny my best gains in terms of muscle mass came from it, though I had to stay on a very aggressive lifting schedule (one that I can't keep up with today due to the lack of time at my disposal).
If you goal is mass, I wouldn't mess with anything other than protein powder or Creatine as a supplement. That's just me, though.
Another thing that helped me move off of "plateaus" in lifting was switching up my routine. I can't stress this enough, as your body will adjust to any long-term lifting routine and it will become less effective over time. I'm to the point where I swith my routine up every 3 months (use different equipment, free weights on some excercises while using machine weights on others, different lifts, etc.). You've GOT to shock your muscles in different ways to keep making gains; at least that's been my experience.
