There's a bit-o'-misinformation around here.
First of all. You CAN get at least 220 HP out of your engine and keep it NA, but it costs a ton of cash. It's been done more than once by guys on this board. Here's what you would need
1. Pulleys - $200
2. Intake - $200 ish
3. Exhaust - $300 - $700
4. Headers - $400 - $1200
5. Cams - $400 - $900
6. Heads - ?? $$$$!!!!!
7. Port n Polish - ?? $$$
8. Managment - $1000 ish
9. Possibly new injectors - ?? $$
Cobb Tuning could give you a real list and a real quote.
I plan on getting to about 200 with just muffler, pulleys, cams, intake, chip/ecu, and headers. I think it's possible and so do many other people.
Second, there are currently at least two chip makers for Subaru and the chips are said to add around 10hp and 10 torque. Only problem is that niether manufacturer can actually SUPPLY dyno numbers, so it's unverifiable. People who buy them are generally happy, though. Chips generally work better on turbocharged engines.
By the time you get all that power NA, you may as well have gone turbo with all the cash you spend, you'll get more power anyway.
I'm going the cautious NA route so that I can go turbo in the future if I chose. Turbo is much more risky because our engines weren't built for it. But it's reletivly safe it you do it right.
p.s. Now everyone who knows more than me can feel free to step in and correct me (hint hint, GTB GUY)