There are loads of options, but the best ones on the market at the moment are:-
Forge Twintake
ITG maxogen
EVOM's
RedRobin has just had the Forge one fitted and has made some healthy gains over his original Carbonio (over 20bhp!!!!)
Similarly the ITG has made phenomenal increases over the stock intake on K04 edition 30's (over 40bhp!!! - bear in mind it is a K04!)
Evoms also has seen increases of over 20bhp too.
If it were my money (even though I have the EVOM's on mine) I'd probably go for the Twintake as it also looks good!