BPU - Basic Performance Upgrades
Boost Cut Controller
Other mods are argued whether or not they clasify as BPU. I've actually had a shop call my FMIC a BPU and I thought that it was ridiculous. It really depends on where you go. On www.mkiv.com, they have a great explanation of everything on BPU cars, they also have kits for BPU.
BPU+ - Same as above with cam gears
BPU++ - Cam gears with underdrive pulley