I've played lots of RPG systems and read even more. D&D is where it's at, at least for me.
One diceless game I read/played was Amber. It's based off the Zelazny books. The idea is that you are a dimension traveling super-powerful guy with lots of intruge in your family.
Character creation is done by bidding. It's something like STRENGTH, COMBAT, ENDURANCE, WILL. I probably have those names wrong, but those are the general ideas. Now, here's where it gets tricky: the players bid on them. The first numbers are a secret bid and then it's opened up. But you only have 100 points. So if you get carried away on STRENGTH you're going to get boned in the other stats. There are also other powers (like dimension traveling) that cost about 25 - 50 points and a few minor skills (like being a doctor) that cost about 4. Being a wizard is ~25-50 and spells cost a few points each.
The scale for these abilites are (and I'm probably going to get these wrong):
Human -> Chaos (weak dimension travel guys) -> 0 -> #
... where # is 1-100, what you're bidding on. One "level" always beats whatever is below, no questions asked. So a Chaos guy is always going to beat a human and a 0-point Amber guy is always going to beat a Chaos guy. Any power gamer worth his salt will immediately note that bidding 1 point on every atrribute is the way to go because you'll always whip up on most other stuff.
Now you play! If you have a higher number in something than someone else, you beat 'em. If you have a higher rank, you really beat 'em (think Darth Vader vs. Biggus Geekus).
I won't go into the setting. But that's how you handle play. Roleplaying and other stuff can modify the situation. For instance, if you have an Uzi and the other guy has a water pistol, the game master may give you an advantage in COMBAT. But there are no hard rules for it, it's very free form.
I played through character generation in high school before I gave up. A buddy of mine played in college and said the game quickly fell apart. But we're both powergamers. So maybe it works well if you have the right group.