Depends what you like and what you don't like, in the first place.
Could you give some pointers? Like, how rules light or rules heavy you are willing (or wanting) to go, what sort of mechanics you'd like to be there, and whether there are any you can't stand (in this context, anyway), etc.
Some references to games you've played or even read, and like (or dislike, too) would be handy as well. . .
It's just that there are *so many* flippin' RPGs out there. srsly!
I'd prefer something on the heavier side as far as rules go. I don't especially like "rules-light" sort of games. I want some crunch, some solid mechanics. Just, hopefully elegant and flexible ones.
I want a system without classes or any other arbitrary restrictions on how the characters are built. Point-based systems are great. I like the flexibility of things like HERO System or GURPS, but those games have perhaps too much crunch density, or perhaps just mechanics which don't seem appealing.
I want something that can model the characters being able to do lots of cool stuff, whether that be involved gladiator martial arts, or complex psionic combat, or wielding magic, without having to be limited to a small list of very specific and limited "spells" or "moves" or "powers" that can only be acquired according to a set framework and used in a certain way.
I want more simulationism and more narrativism, and less gamism, compared to D&D.
I like dice pools, I like opposed rolls in combat, I like less swingy-ness in the resolution system, and more emphasis on the characters' capabilities and decisions, less on luck. The d20 is not my favorite system of resolving actions. I hate percentile, too. I can't say that I especially like games where you roll on tons of charts, either.
I like mechanics which reflect the characters' backgrounds in important ways. Lifepath-type systems always seem cool to me. Or personality/psychological elements to a character which have real effects on gameplay. Spiritual attributes, beliefs, nature, stuff like that always intrigues me in a game.
I want gritty, tactical, and crunchy combat, but also mechanics that emphasize role-playing and characterization, and make those things actually matter in a concrete way in the system.
I like advancement that lets the characters improve in whatever specific ways they want to, rather than just throwing standard blanket upgrades on everyone as they "level up".
I've played all editions of D&D, mostly, plus Champions, the Palladium family of games, World of Darkness/Storyteller, Shadowrun, Earthdawn, Warhammer FRP, Cyberpunk, and Star Wars. (Older versions of all of those except for D&D - not any newer editions from, say, the last 10 years.)
Shadowrun was probably my absolute favorite. I like the flexibility of HERO, but not really the way the game actually plays. I liked Earthdawn too, and old Star Wars a bit less so. Not too fond of Palladium, Warhammer, or Storyteller.
Games which I'm very intrigued by the idea of but know little about are Burning Wheel, Riddle of Steel, and the newer HeroQuest.
I don't mind doing some work adapting a game to Dark Sun, making house rules, creating the appropriate races and magic system myself based on the core ruleset. I just want a game basis that I like a lot, which is flexible yet has a lot of its own cool style and fun mechanics.
Lots of suggestions here though, already. So I'll start looking into some of those.
Thanks!