Ars Magica is a fantasy rules system and campaign setting which emphasis magic and wizards above everything else. There is no attempt to balance Magi characters with mundanes - magi are simply more powerful and generally flexible in all but a few situations. It is published by Atlas Games.
The game backs this up with a detailed and comprehensive magic system, which is second to none. The flexibility and detail available to players when designing and player magi characters is extensive, and makes Ars Magica one of the best game systems available. The game is focussed on the overall campaign spanning decades if not centuries - magi learn, adventure, build up their powerbase and eventually grow old and die over the course of it
Even for those who have no intention of actually playing the game, it is worth getting just to mine it for ideas.