I'll second Lifepaths, and since Mekton Zeta is early ninties, it just makes the cut off.
Speaking of Mekton, two elements of that. MTS, the construction system is everything I want in a 'gear system'. I can build anything from a knife to the Death Star in it without resorting to anything more then basic math and in a straightforward logical fashion. No cube roots or doing things in unintuitive orders like GURPS Vehicles.
The second is the differentiation between character types. A PC is either a Rookie, a Professional, or a Prodigy. Rookies have a limited number of skills and start play with low scores in them, but get double advancement points for their package skills. Professionals have many more starting skills and more points to spend on them, but advance more slowly. Prodigies have the same number of skills as a Rookie, but get triple advancement in one or two skills.
I'm not sure I'd call it a RPG, but the game bills itself as such, so Dread's jenga based task resolution is incredibly atmospheric.
Deadlands entire system was hokey with it's mix of dice and poker hands, but was really fitting to the setting.
L5R's dueling mechanics took me and my players a little to get our heads around, but once we did it really captured the tension of the act.
I've recently be digging Eclipse Phase's mechanic. It's a pretty straightforward percentile system, but I can run it straight off the GM screen and Moxy is a cool action point system. Similarly the reputation based gift economy is very well done.
Dramatic Conflicts in SC2.0.
Teenagers From Outerspace's Too Much is Too Much mechanic. Roll too well and you succeed, but things go awry as well. Very much in the style of the source material.
Paranoia's dramatic combat system. Entertain or die. Actually, pretty much the entirety of Paranoia's PC mechanics. And it's GM advice.