why dont you tell us what kind of mk3 you have, turbo or n/a?
there is a ton of aftermarket stuff for mk3's, i can not list it all. it just depends on how much you have to dump in to it and what hp range your after.. tell us how much you have to spend im sure some ppl here can help guide you..
look at
www.horsepowerfreaks.com, then select you vehical and they will show you what parts they have for your car..