Ooh, great thread idea! I have a lot of ranged weapons that I like, so apologies if this list is a bit long.

I put a short description beside each one for convenience. I definitely have a preference for bows over guns. I usually don't like crossbows very much, but there's a few I love.
Bow:
•Ancient Bone Bow / Striker's Mark:
http://www.wowhead.com/item=18680 /
http://www.wowhead.com/item=17069 (skeletal)
•Black Bow of the Betrayer:
http://www.wowhead.com/item=32336 (large, spiky, green orbs)
•Wrathful Gladiator's Longbow:
http://www.wowhead.com/item=51394 (green, spiky, skull face)
•Bow of Taut Sinew:
http://www.wowhead.com/item=21478 (purple and spiky)
•Bristleblitz Striker:
http://www.wowhead.com/item=30906 (bluish/bronze with green glowing face)
•Brutal Gladiator's Longbow:
http://www.wowhead.com/item=35047 (purple with silver accents, green orbs)
•Crypt Fiend Slayer:
http://www.wowhead.com/item=49844 (blue, runic, dragon faces)
•Mandokir's Tribute:
http://www.wowhead.com/item=69625 (green serpent)
•Zod's Repeating Longbow:
http://www.wowhead.com/item=50034 (grey-blue, spiky, skull face)
•Valanos' Longbow:
http://www.wowhead.com/item=31303 (tealish-green with purple accents)
Gun:
•Brutal Gladiator's Rifle:
http://www.wowhead.com/item=35075 (spiky, dark purple/black with green accents)
•Don Santos' Famous Hunting Rifle / Gyro-Balanced Khorium Destroyer:
http://www.wowhead.com/item=31323 /
http://www.wowhead.com/item=32756 (dark purple/black with bronze and green accents)
•Dragonbreath Hand Cannon:
http://www.wowhead.com/item=19368 (red dragon head)
•Envoy of Mortality:
http://www.wowhead.com/item=40385 (black, spiky, skeletal spine)
•Widebarrel Flintlock:
http://www.wowhead.com/item=47883 (black cannon with red runes)
•Legion Blunderbuss:
http://www.wowhead.com/item=24389 (spiky, bright green accents)
•Nerubian Conqueror:
http://www.wowhead.com/item=39419 (black with spiked metal)
•Veranus' Bane:
http://www.wowhead.com/item=45137 (black/red 'steampunk')
•Wolfslayer Sniper Rifle:
http://www.wowhead.com/item=28581 (simple black with vine-like details)
Crossbow:
•Amanitar Skullbow:
http://www.wowhead.com/item=43284 (brownish horned skull)
•Arbalest of Erupting Fury (heroic):
http://www.wowhead.com/item=71414 (purple with fire accents)
•Dragonheart Piercer:
http://www.wowhead.com/item=63532 (purple with dragon face)
•Felglacier Bolter:
http://www.wowhead.com/item=50262 (bright blue, runic)