Some help you guys have been.
Anyway, onto the juicy stuff. Now Oldman does have a point: headers alone won't necessarily help out your car, and what you want is more torque (at least initially) to help propel that fat-ass Camry.
Also, like what was stated earlier, a full exhaust setup would give you some considerable gains, but just to let you know, it's not like it's gonna enhance your engine's performance through the roof. Like you yourself said, headers help the engine to breathe better (intake inhales, exhaust exhaules [heh, notice how they both start with "in" and "ex?"]) Anyway, basically all aftermarket exhaust headers would do is help the engine exhale a little faster.........right through the rest of the *stock* exhaust. So that's why, if you want good power from your exhaust, you're gonna have to do more than just add an aftermarket exhaust header.
One way I like to think of it all is, is that it isn't just the part itself, but the sum of the parts that make the greater whole.
Unfortunately, I'm not as familiar with product availability with the 3rd generation of Camrys as I am with the 2nd. Go to SC3 (Southern California Camry Club) and look around in there. It's a great website for all generations of Camrys and is a great starting point.
Anyway, hope this helps you some. Good luck against the evil Civics!
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It's not what car you have, it's what you do with it that matters.

Packing your lunch in a paper bag-$5.00
Eating your lunch you bought on an airplane-$50.00
Losing your lunch from the airplane's cuisine, but not having a paper bag-Priceless
For everything else, there's paper bags!