Stainless steel headers
 

Do these look any good
Has any one bought any
eBay.co.uk: Subaru Impreza WRX STI Exhaust Manifold Header HKS Styl (item 180112986181 end time 08-May-07 22:45:44 BST)

Buy some proven ones imho.

GT Spec or Gruppes

GT spec available from Mocom Racing - Performance car and trackday products amongst others

I had a set of the origional Gruppe-s headers from the group buy a few years ago. They were very good apart from the two bolt flange style where the up-pipe meets the collector box, Loads of people including myself suffered with this joint blowing, this used to happen repeatedly especially when running higher boost (1.5 Bar + Etc).
I cured mine for a longer period of time by doubling up on the gaskets, others cured it by welding the flange :D
This problem may well of been sorted on the later gruppe-s headers, But on that i cannot comment.
I would advise to go for a 3 bolt setup & always avoid the two bolt scenario, With a 3 bolt flange, you can fit & forget ;)

http://www.stiracing.com/product/298.jpg
Simon Tecnica International Racing

Dean