A run down of good systems I've come across, and a little about what I'd like as a gamer (for myself):
1. Menu based timed turn based combat. Kinda like the various Final Fantasy games. I think the best I've encountered in that genre was Chrono Trigger and Final Fantasy Tactics. Both incorporate a sort of terrain and positional effect, and I especially like Chrono Trigger's combo attacks between two or three characters.
2. Click and hit with pause and pick. Kinda like Secret of Mana or Planescape: Torment. Typically select a character or party, click a monster, they attack it, and if you need special abilities or items, there's a pause-out function where you can pick one.
3. Console or combo based. Typically a very action and skill oriented battle system, in which you control a single character, and the combo buttons you use determine what kinds of moves and hits you land. B B B B+A UP DOWN+A-hold-RIGHT+A take that evil doer! It's especially fun when you "unlock" new combos as you go. I'm thinking kinda Soul Calibur and Zelda here.
4. Aim and fire. The Fallout series is good here. Shoot shoot shoot, and if you need help aiming, that's what the PIP boy's for, pause and assess where the weak spots are and hit them with a weapon they're weak to!
5. MMO or ability based. Hotbar or action keys linked to various abilities, usually with a click and hit element. Generally it's good if movement is governed by a different system than the abilities (stupid Diablo 2 sorceress, stay in the back and SHOOT the monsters, you're not a melee dumb girl -- gah killed by a lightning bug AGAIN
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SO again, what kind of RPG you want to make? Party based? Single character? Multiplayer?