Pipe - the choice is yours
Re-chamber head - there are variations of the type, but i think a KOR basic is plenty good, dont need no fancy hemi cut or whatev ($60 from KOR)
Lighten flywheel - as the title says. i forget what ken charges, but its for faster reving
Porting - this is where its at. lot of gain here. many different companies will do them ranging from about $150 to $300. KOR, Flotek, or REP (KOR is most common)
if you want power and want it usable, you will need better suspension
Shocks (front) - works, elkas, any name brand. it just depends on what you are willing to pay. used works for under $300, new elkas $1000 or more
Shocks (rear) - 400ex or 450r swaps easily. people say they are better, but i didnt like either. also same options as above.
Width (front) - best option, extended a-arms($300+). cheaper alternative, diamond j widening kit ($200) or stud spacers ($40)
Width (rear) - best option, extended axle. banshee axle is a good one. cheaper alternative, stud spacers
you may also want tires, but there are so many i wont even go there
turf tamers suck, and i like Tech4 STI tires. but thats my preference