Notice: newer version of IC2 don't use Crop IDs anymore. This list is kind of useless
This is a small list of known addons/mods that use up crop IDs, and what they use.
IC2 currently uses 0-23, but I'd avoid 0-39 for future expansion.
IC2 Classic (Immibis) currently uses 0-21 (conflicting with IC2). There's probably not a need to worry about expansion.
SkyTech Crops currently uses 40-59, but I'd avoid 40-80 for future expansion.
GregTech currently uses 124-142 and 145-149, but I'd avoid 124-199 for future expansion (gap is because the red and brown mushroom were moved to IC2).
IndustrialEx currently uses just 200, but I'm reserving 200-350 (I has big planz :3).
Please alert me if I missed an addon (or another mod), or if you're working on a mod/addon, or if anything is incorrect. If you're working on a "secret project" you can PM (I totally will not tell anyone, unless they pay me big bucks :P)