Well With out spending big money you wont see big power however.
Brakes - Brembo HC/max, Ferado DS2500, Braided lines
Remap - Live at RStuning or TDF or a generic RStuner map (fastchip.nl) or JMS offer a varient of this map.
Suspension - Eibach Sportlines if you just after decent springs, or a set of H&Rs or equivelent mid range coilovers.
Induction - V6 airbox, maxogen or a panel filter.
Weight saving - Simple Free BHP
Exhaust - Yozza, Miltek or a custom one from a decent sustom exhaust builder..... Decat?
Matched inlets, If you have RS stamped ones you wont see as much gain but no stamped inlets always see a good gain.
And lastly a good servic