I would recommend FATE
unreservedly. I'd also start by reading The Fate 2.0 pdf
and the pyramid reloaded pdf
(both free) to get the concepts before reading through the more recent Fate 3.0 (Also free).
Fate is based around "Aspects" of characters, scenes, situations, and items. The aspect mechanics allows the spirit
of a thing to be used within the game mechanics. Understanding Aspects are keys to getting on with Fate.
For example aspects, here are some straight from the websites:
Relationships (Mama's Boy, Chosen of the Dread Lord)
Beliefs (The Lord Is My Shepherd, Nothing Is Forever)
Catchphrases (Can't Keep My Mouth Shut, "It's Not My Fault!")
Descriptors (Wiseass Wizard, Rugged as the Road)
Items (My Vorpal Sword Goes Snicker-Snack, My Lucky Rabbit's Foot)
Pretty much anything else that paints a vivid picture of the character (Big Man On Campus, Anger Is My Constant Companion)
Aspects are also juicy ways of anchoring characters into a story, and the more interesting aspects will have lots and lots of implications:
Tasty: Trained Fencer.
Bam!: Trained by Montcharles.
Tasty: Strong as Ten Men.
Bam!: Strong-Man in the Circus of Crime.
Bland: Dark Past.
Tasty: Reformed Evil Cultist.
Bam!: The Ebon Shroud Cult Wants Me Dead.
It has a mechanic for Compelling and Invoking aspects, whereby compelled aspects earn you fate points
but cause negative consequences, and invoked aspects loose you fate points but generate a positive effect in the game.
For example, you could invoke
the aspect "Trained by Montcharles" to improve your chances of success in a swordfight, but the GM could compel
the same aspect to get you into a duel at dawn because of Montcharles's reputation. You could also invoke this aspect when dealing with the opposite gender, to improve your chances in the social arena, but the GM could compel you to aid your old mentor when he's in trouble, even if it would be detrimental to you. The richness of aspects, and how they improve storytelling and encourage role-playing is something I haven't seen done as well in any other system.
It's also simple enough that the entire thing can be explained in under 15 minutes to a table full of people that have never role-played before.
There's a few commercial games based on Fate too: "Spirit Of the Century" and the Dresden Files RPG. Both are great fun and give more polish and context than the open source docs do.[EDIT]:
I have some interesting drafts of several complete magic systems using Fate somewhere if you want to talk more about magic and the existing systems in the open source docs are unsuitable...[EDIT2]:
Fate games have been repeated award winners: The Dresden Files RPG won several golds at the ENnies 2011: Best Game, Best new game, Best rules, Best writing. As well as two silvers: Product of the year and Best production value. Diaspora, another Fate game, won the 2010 Best Rules.