Crossbow
exotic
Accuracy: +3, with +3 per Eagle Eye instead of +2
Damage: 3d6
Ammo: holds 1 quarrel
Reload: 1.5s
Pistol Crossbow
exotic (counts as a pistol)
Accuracy: +5, with +3 per Eagle Eye instead of +2
Damage: 2d6
Ammo: holds 1 quarrel
Reload: 1.0s
Autocrossbow
unique
Accuracy: +3, with +3 per Eagle Eye instead of +2
Damage: 3d8
Ammo: holds 5 quarrels, fires 1. needs to be pumped like the combat shotgun (a step or reload)
Reload: 0.5s to load a quarrel, 0.5s to pump. (an empty weapon would need both a reload and a pump)
Alt-fire: fire all quarrels, 3 seconds, with an accuracy penalty (-3)
Alt-reload: full reload, 2.5s.
Whenever a Quarrel hits an enemy, it gets added to that enemy's inventory. If it misses, it appears on the floor. The first time you pick up any crossbow, you get a stack of quarrels (10).
Alternately, half-life's sniper crossbow could be neat. But there are a few auto-hit weapons already, and my main motivation was the idea of being able to recover your quarrels; molten steel doesn't make for good recovery. :)
I'm really not sure on the damage of these, could be too high or too low. Their main drawback is the inability to keep shooting, like the shotguns but moreso since you'll never have many quarrels.