I have read and heard good review(s) about Whiteline, Cobb and Perrin. I hav also heard recommendation that you should also replace your endlinks while you are at it. As far as that goes I have heard Mosc say to stay away from Cobbs front endlinks just becuase they are noisy. As far as recommendation goes kind of depends on what you actually want to spend on one, I wouldnt go with some ebay brand, I personally am kind of partial to Cobb. Just my two cents though.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX