You asked so here's IMHO:

Cheap low Performance:
FMF Gold (Stamped)
FMF High rev

Medium Can work good & be bought cheap if you look:
Bills Pipe (Torque, drops off in 3rd gear)
Trinity (Mostly drag, not a lot of low end)
LRD/LED  (can be bought new)
Paul Turner (really good all around, stinger needs to be enlarged with more than stock porting, Can Be bought new)

Big Boy Stuff:
Aaen (cheapest, quality lacking)
DCS (Getting better torque & peak numbers than Q but does not rev as high, haven't seen the quality 1st hand)
Q V-1, V-1.1, V-2  (Best flat land, no weight, drag pipe I've ridden 9.4K RPM)
HPR (Best all around power monster, best incline drag pipe, widest power range, pulls the hardest)