UPDATE EDIT: Actually, I'm trying to think of a good fantasy example where everyone's the same level and I'm blanking. Maybe they're all just copying LotR, but with the few exceptions where a couple 'kids' go off by themselves there's usually a mix of levels/experience.
This is in no way a thread crap, but:
The Chronicles of Prydain
The Chronicles of Narnia
The Malazan Books of the Fallen
The Outlaws of Sherwood
Dune - if you count it
The Chronicles of the Black Company - for the most part
The Wheel of Time - there are exceptions but once you get past the first book most people who are actually adventuring together seem to be of similar level
The Song of Ice and Fire - not the whole series, mind you, but there are many instances of skilled groups rather than powered troupes
The Dies the Fire series
A good bit of the Heralds series
The Rhapsody Series
Classical Precedents:
Arthurian Literature
The Song of Roland and The Matter of France in general
The Iliad
Baron Munchasen and his Clever Servants
Romance of the Three Kingdoms
Journey to the West
The Outlaws of the Marsh
The Canterbury Tales - in a very oblique and non-adventurous way
The Henriad - not all characters are equally bad-ass, but I'd say Fallstaff is as high a level coward as other characters are true knights
The Seven Against Thebes
Jason and the Argonauts - at least once Hercules has left