There's a bunch of good pipes. I've had Akrapovic and Yoshimiura recently and loved them both, Dr.D makes good stuff .
Where are you from though ? If it's a California bike you should plug or remove with a kit the smog pump, via one of the kits in the online store here.
If you don't fix the jetting and open up the airbox SIMULTANEOUSLY a pipe is a waste of money,and aftermarket pipe or not your bike is nowhere near where it should be because it is way,way too lean. If you add a pipe to that too lean stock condition your bike will run like crap and also run too hot.
Here's the easiest way :
http://www.crfsonly.com/catalog/product ... ts_id/1093?
http://crfsonly.com/howto/450x/airbox/c ... airbox.php
http://crfsonly.com/howto/450x/jetting/ ... needle.php
Remember,
simultaneously. The jet kit has great directions,follow them,and enough extra jets for just about any combination of modifications you can think of.
Doug