I guess it's my turn...

I've been riding my Trek 3900 bike pretty hard for the past few months. I've learned to like some parts (brakes were actually decent), and hate others (derailleurs, fork). Iim taking this to school with me and I want to buy a trails mtb between $500-750.

I'm mostly on trails with a few smaller (2-4ft high) jumps, lots of logs between 6"-2ft. I just want something that's quality and doesn't screw up every time you try to shift it.

Any ideas what would suit me best? Lighter would be better, but I just want something quality. Also, what size frame should I get? I'm 5'8" 155lbs (looking to bulk up to 165ish).

Thanks,
James