If you're modding on a budget (as I am!) here's my suggestions and rationale for the order in which to mod:
(
apologies if I'm preaching to the converted!)
1. Wheels - lower profile tyres will give an immediate feel of improved handling due to less body roll (actually less flex from the sidewalls) in the corners (I bought my Monty IIs
and put 2 tyres on for less than ?350)
2. Suspension - (try to do shocks at the same time as the springs) will compliment the tyres and further improve handling
3. Brakes - no good improving the handling if you can't slow down/stop properly!
4. Re-map/chip/box - without the others you'll have something that flys, but you'll scare yourself silly 'cos it won't stop or go round corners......[

]
5. Spoiler - do you really want a spoiler instead of performance mods....[

]