Thinking about what I've run...
GW Judge Dredd. The lightest rules game I've enjoyed running. 2nd or 3rd best Adaptation of a non-RPG IP to an RPG, IMO.¹ Nothing like a random block search to kick off a game... but the 39D table is in the companion. I really wish GW would let whomever the current licensee is rerelease the GW one in PDF...
Others I consider worth running again because of mechanics: RuneQuest 3rd (aka Avalon Hill Rune Quest), Mongoose Rune Quest 1, Spacemaster, Rolemaster, Justifiers, MERP (but as a general fantasy, not as Tolkien).
Ones I want to try yet: Revised Recon/Deluxe Recon, HARP²
Ones I'm tempted to run despite the mechanics: The Mechanoids³.
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¹: ALIEN is definitely my pick for Best Adaptation; it's not a d100 game, tho'... Depending upon how it plays, Blade Runner may eclipse Dredd. But also not a d100 system.
²: It's another spawn of Rolemaster... but I've yet to actually read it through....
³: Either the trilogy or the standalone, but NOT the Rifts version.
The Troubleshooters (Similar system used in a few other Swedish RPG'S. It is built upon the system used in Järn, and Hjältarnas tid, and also used in Kopparhavets Hjältar.)
Call of Cthulhu (not quite sure if I prefer the older versions, as it was too long ago since I played them, or 7e) / BRP