I posted here a while back and got some good advice. I have a Celica SX (5S-FE) that I am really enjoying. I put a K&N Filter replacement in and have noticed that the revs are smother and easier especially between 3K and 5.5K - which was good.
Next step is an EXHAUST replacement. I want it to look and sound decent but the priority is performance increase. I have got all kinds of quotes but Performance Exhaust in Ringwood (VIC) seemed most knowledgable so far. Catback system $390 and some extractors (which he would have to make, apparently) for about $300. He suggested a 2.25 inch muffler.