Exhaust and extractors will most likely give around about 15-20% more power, as well as a mean exhaust note
Look at some induction mods as well, to get more air into the engine. Cams are ok, but are also expensive if you don't do them yourself.
Try and stay away from headwork until the last resort. Explore everything else first..
A bigger diff will get you better take off, if that's your thing..
Seeing as though you've just done your head, i wouldn't muck around with it too much. Wait until the gasket blows or something and do some headwork while it's off..
Colour code everything, it looks 1000 times better on EA-ED cars. Handles, mirrors, bumpers, the works. I like Simon's (Bass_Crazy's) as an example, and even sunny's is looking shit hot.
Good luck mate, and get a second job, cos once you start, you won't be stopping