Well,light and tricking don't really work together all that well.You'll have to compromise somewhere.For tricking you'll want something solid,but solid means heavier.Low end Steel frames might be something to look into(high end steel tends to have thinner wall tubing which makes it light but not so good for abuse).Another option is alu.Lighter than steel,but the same deal(compare 6061 tubing to 7005).Also the fork is a issue with alu frames.Carbon rides nice but is not the best for harsh tricks,aluminum forks are solid but give a harsh ride and steel forks kinda look out of place as most aluminum frames tend to be oversized tubes.