The most of basic of shortbows. An aquatic longbow underwater, or maybe a short version of it.
Special ammunition, such as the blunt arrows from "Races of The Wild" also have reduced range increments.
I don't think a small shortbow reduces range increment, though...
As per
http://www.d20srd.org/srd/equipment/weapons.htm#weaponDescriptions, going from medium to small does not lower the range increment. Going from longbow to shortbow does though.
It used to be that smaller ranged weapons had shorter ranges (and larger ones longer) in 3.0. For example, on page 4-5 of the Arms and Equipment Guide it says:
"Size and Range: Larger and smaller versions of
ranged weapons have correspondingly longer or
shorter range increments. Each time you increase a
weapon’s size, lengthen its range increment by 25%.
For example, Huge longbows, such as those wielded
by ogre mages, have a range increment of 125 feet.
Each time you decrease a weapon’s size, shorten
its range increment by 25%. A Medium-size longbow
in the hands of a halfling has a range increment
of 75 feet."
The weapon size rules in this case refer to the size of the weapon itself and not strictly who it was meant for. A 2h weapon like a longbow was typically one size category larger than the user, hence the huge for a large creature and medium for a small.
