One traditional split goes like this:
Back + biceps
Chest + triceps
Legs + shoulders
however some people still have enough juice in them on chest day to do shoulders, so they prefer:
Back + biceps
Chest + shoulders + triceps
Legs
and abs will (usually) be thrown in on at least 1 or 2 of those days.
HOWEVER, considering that most back exercises hit your biceps in some way (i.e. pull-ups, pull-downs, rows, deadlifts), and that most chest exercises hit your triceps (i.e. bench press variations, dips, etc), some people prefer to swap the muscle pairings around so that they can get the most out of their arm work without them being fatigued from assistance in other exercises. That is,
Back + triceps
Chest + biceps
Legs + shoulders
Personally I think it's a good idea, and it is quite a commonly used one.
My split is back+biceps, chest+triceps, and legs+shoulders. For *best* results, maybe the above is perhaps slightly better.
The opinions of everyone else would be good to hear
Cheers,
-shaun