Keeping in mind that I am NOT a crossfitter by any means, as a 265 lb powerlifter who does cardio, cordygen 5 has done wonders for me. It makes you feel like you're about one or two levels of conditioning better than you really are, which allows you to train harder, which gets you into better shape... the first time I tried it I was just starting to do cardio again, and went from 1/2 hour dripping sweat on the elliptical to being able to hold a conversation and cruise along, instantly. Wondering if it was a fluke b/c at the time my conditioning was so poor, I gave it to a friend who is a very high level tri-athlete, and successful trainer. He sent me a text which stated "holy **** this stuff is no placeabo", he took about 30 seconds off every mile on a 10 mile run. That's just the cordy 5. Millennium has lots of other options, but I'd start with that.
Something you may consider, outside of being a crossfitter, is the mycogreen. Why do I mention it? Because I've been taking 6 caps/day, and it's done wonders for how I feel in general. No performance benefit directly (much like a multi vitamin, despite what people say) but it has to help, as more often then not, I feel good and ready to train.