If I decide to run an actual campaign, I'll be using the only system I really love -- HERO System. The only book you'll need (and you really won't need it) is the HERO System Sidekick. When I run HERO System, I prefer to build the characters, so I usually just have players write up a two or three paragraph description of their character and his/her background and then I translate that into rules. HERO is an extremely, extremely complicated system to really master (the main rulebook weighs like 5 lbs and is three inches thick!), but it's pretty easy to use if you don't have to build your own character (which is why I prefer to build the characters, new players tend to create very suboptimal characters and waste tons of points). My favorite thing about HERO is that its an effects-based point build system, so you can literally make any kind of character you want. Its far more flexible and allows for much more well-rounded characters, especially the sort of jack-of-all-trades fighter/rogue/magic-users types that are common fantasy heroes.
And no, we're not starting Tuesday.