Reading that other thread about 43 "Easy" HP gains, gave me an idea. I want to create a list of things people have done to their car, and the benefits. It doesn't have to be raw HP gains that are listed. There can be other benefits. If this list becomes comprehensive, then perhaps it can be made sticky so that we can decide what we want to do next to our cars. Here's my list personally:

2 x 2.5" Straight through mufflers
Approximately 8hp gain over entire RPM range. Slightly higher mid range gains (Also nasty nasty noise from exhausts. Had to sound proof boot, doors and floor to get from painful, to merely annoying.)

Larger K&N Air Filter
Approximately 2hp gain over entire RPM range. Throttle "feels" more responsive.

Fuelstar Detonation Reisistance Device
Bugger all. May have let me advance timing more than without it, but no proof

"Perfect Power" Full Engine Management System

Fuel Mixture Enhancement
13 horsepower over most of the RPM range. Some areas could not be tweaked so significantly.
Allowed Nitromethane to be mixed in with fuel. Waiting to retune for best results. Expecting a further 10-15 horse power with 1% Nitromethane mix.

Ignition Timing Advance
0 to 3 degree advance during tests. Still waiting for final results

VTEC Engagement Point Move
Not tested yet

The next mods I would personally like to install and so would like to hear of other people who have already done them are:

Injen CAI
Jet Hot Header Coating
Koni Adjustable Shocks
Progressive Springs
Better Brakes
Bore out Throttle Body to 70.1mm
Spoon Cross Brace
Port and Polish
Intake Header spacer (Insulates the header from the body to reduce heat?)