R2D2!
Especially from Episodes 1,3 and 5.... R2 was Cool.
Got holes shot in your spaceship? An autopilot that won't take "No" for an answer? A bad case of buzz droids? Whether your ship sunk in a swamp or you got a busted hyperdrive, R2D2 will open that door, turn off the blast furnace, fix this, adjust that or even staple 3P0 back together just in time to deliver lightsabers or help blow up death stars.
The "Clanker" Battle Droids are more silly than cool but some of General Grievous's personal Guards are pretty cool...you know, the ones that keep fighting after you cut their head off and stay in one piece after the first couple of lightsaber strikes.
Marvin The Paranoid Android as "Cool"? Eh. He's too depressed to be cool. The Hitchhikers Series is cool.
Even cute, schmaltzy, malfunctioning Waste Allocation Load Lifter Earth class droids are cooler than Marvin. Sirius Cybernetics just doesn't do "Cool".
Speaking of Wall-E.... Extra-terrestrial Vegetation Evaluators are Cool. Even clumsy little Burn-E welding droids don't do badly.
I thought the "Old" robots in "I, Robot" were cool. Not the new, fancy Killer Robots, not even Sonny... but the old, discarded robots ("RUN!") trying to save the humans from the new ones... those were Cool!
Of course The Terminators were Cool. Bad ones, Good ones, even the liquid metal ones..... all Cool. Did they not count because of their artificial living tissue covering? The droid inside was a robot, not a cyborg....
Other ones i'm not sure if anyone's mentioned:
Fembots from Austin Powers
The Evil, Killer Bill and Ted robots from the future
Rosie from the Jetsons along with Uniblab and also the poor, befuddled dance instructor robot.
Have Fun,
Keri
PS. Anybody want to start threads on "Favorite Movie Computers" like HAL and "Favorite Movie Cyborgs" like Davros?