D20 Modern! - I love the idea of intermediate classes (i.e. Advanced classes) between 1st level characters and focused prestige classes. Now if only it was redone with what we've learned akin to the transition from AD&D 2nd edition to 3rd edition D&D. Because attribute based generic classes are stupid (e.g. Strong, Fast, &c) I wish we'd see a major revision to D20. With that in mind I'd really enjoy 4th edition D&D if it were a blend of D20
v.3.5 and Modern.
Other, lesser systems that didn't catch on: Amber Diceless Roleplaying, Shadowrun, Robotech (by Palladium), Warhammer Fantasy Roleplay, and Purgatory.

Other, lesser systems that didn't catch on: Amber Diceless Roleplaying, Shadowrun, Robotech (by Palladium), Warhammer Fantasy Roleplay, and Purgatory.
