I've only had a few:
Both of these had art or at least digibashes that I don't have handy at the moment:
Foxfire - a fox Maximal repaint of the Wolfang mold in the BW era
Slipstream - a black Decepticon repaint of Space Case. Actually used this one in a forum RPG for a bit. Hadn't done anything with him in years, especially since there's a more prominant Slipstream now in official fiction...
Lastly, inspired by the idea of fantasy-themed Pretenders, I created my own set, who essentially crashed on an equivalent of Pathfinder's Golarion, and are hunting Decepticons they were chasing who took on pretender shells based on D&D monsters. Which of course means that they became an adventuring party to give them a cover to track rumors and hunt the 'cons down. I've considered art of this group, but I'd want to commission it and to do that I's want to work out transformations and find appropriate artists.
Hardrock - The hard-nosed leader of the group. Dwarf pretender shell. Altmode is a H-tank. Brown and green color scheme, uses an axe and has a viking-looking head
Strata - Personality similar to Lander form Masterforce. Elf pretender shell. Spaceplane alt mode, with a blue and gold color scheme. Uses a "laser foil" like Captain Harlock's rapier
Foxfire(yes, I reused the name) - The resident hot-blooded rookie. Female, with a kitsune pretender shell. Dragster alt-mode. Shell has a red/orange/yellow scheme, was considering making the bot mode white/gold. Uses a energy crossbow.
Unnamed as of yet - Overly curious and naive young scientist/medic. Cleric-themed pretender shell. Alt mode is a helicopter, and robot mode has a cockpit chest.
Other unnamed member - Didn't really nail a personality fully down for this one. Armored riding cat pretender shell. Robotic panther alt mode. Often forced to be left at the stables, and has a constant chip on his shoulder about that and being forced to be treated as a mount by the group when among the general population.