Multishot (previously Killshot) is a tiny addon that automatically takes a screenshot (with interface) whenever you kill a boss, gain an achievement or level up. It currently supports all dungeons/raids up to Patch 3.1 and works on all locales.
Check out the new config options (Interface > Addons > Multishot).

Multishot 1.0
- now using LibBossIDs-1.0 instead of own database
- added: config options (Interface -> Addons -> Multishot)
- removed: screenshot on level up for hunter pets
Multishot 0.7
- added: new Ulduar boss ids, thanks to: droeber
Multishot 0.6
- added: screenshot on level up for hunter pets
Multishot 0.5
- added: complete WoTLK dungeon/raid data
Multishot 0.4
- added: "Headless Horseman" from Scarlet Monastery (event boss)
- added: "Prince Tenris Mirkblood" from Karazhan (event boss)
Multishot 0.3
- added: some WoTLK dungeon data
- fixed: no screenshot was taken if player died during boss kill
Multishot 0.2
- renamed to "Multishot"
- added: WoTLK compatibility
- new: taking screenshots of achievements
- new: taking screenshots on level up
Killshot 0.1
- initial release