you can get small, but decent gains from upgrading things like the intake, throttle body, header, cat, and all the exhaust piping for better flow. you'll see slight horsepower and torque gains.

as far as swaps, it all depends on what you're willing to spend and what you plan to do. there are a lot of different swaps. research all of them, i believe there is a thread somewhere about them. mini-me swaps, B16s, B17s, B18s (GSR/LS), LS VTEC, CR-VTEC, F22, H22, H23, K20s and beyond.

if you ware thinking of a turbo kit, consider which motor you'll be using. some are yeild better gains than others, while some are easier to set up than others. don't forget.... whatever motor you use with a turbo kit is going to need the internals ungraded, fuel system upgraded, and ECU upgraded. deffinately try searching for swaps and turbos... don't try to throw something together w/o research. you'll be glad u researched.