Scimitars can be great if you're looking specifically at damage and critical range; however, without even going into the expanded material, PH has certainly streamlines many weapons for additional abilities like:
sickle: trip (I always love tripping)
Flail: Disarm, Trip (both useful)
Trident: Brace (because you never know just what your DM can throw at you)
Whip: non-lethal, reach, trip
On top of these special abilities, daggers are now both useful for melee and as thrown weapons, and with can be hidden in a weapons check using slight of hand...food for thought anyways. Kukri's also have that 18-20 crit range although I generally prefer the dagger idea because a few points in slight of hand can take you a long way.
This always depends on the build you want to make, but I felt there were a few extra options to think