Probably MK-9 augment kits. Depends on the server but they're usually pretty profitable.
That would require cybertech as well for the most cost efficient.
Endgame synthweaving (if you do not have cybertech to feed it components) is all all about augments. Augment schematics are acquired through slicing but they are usually dirt cheap on the GTN: less than 5k each. There are five versions that Synthweaving and can craft:
- Might: Strength and Endurance
- Resolve: Willpower and Endurance
- Redoubt: Defense rating and Power
- Alacrity: Alacrity rating and Endurance
- Command: Presence and Endurance
But only the first three are really worth making: Might, Resolve, and Redoubt (you might find someone who wants an Alacrity every now and again, but don't count on it; and I have never seen anyone who wanted Command Augments). The best available grade is 28.
The schematic you purchase will get you the green/premium version, you have to reverse engineer to get the blue/prototype and the craft and RE blues to get the purple/artifact.