intake, exhaust, headers, m3 cams, Chip it, good set of coilovers or lowering springs with struts, urethane suspension bushings, stiffer clutch, underdrive pulleys, etc..... any of those are options for performance upgrades, not all you will get for under 2g's though. So make your choices wisely... Intake, exhaust and headers are your best idea for making hp, as well as getting a chip after you have those mods already installed..
What about only for engine torque? In other words, what would be the first 5 things you would replace/upgrade to gain the best torque gain, considering budget. As it is now, my car is completely stock. (98 323 IS)