FS1/2 - a few mediocre missions and table changes
Civ2 - New rulesets and units - a Dune mod that I never finished
C&C, RA1/2, Tiberian Sun - New rulesets, units and weapons
Total Annihilation - Tons of units all moddeled and scripted
Alpha Centauri - New factions and rulesets
GalCiv - Tons of ships, improvements etc...
Homeworld/Cata - Changing a few ship tables
Moo3 - New rulesets, spreadsheets, abilities etc...
The only thing there thats harder than 'trivial' is the TA thing, almost everything else is just txt editing