I have a mod that i use in game but it dosent update all that well and dosent show stats on all items what i like to do is go to http://www.wowwiki.com and then go to the instance look up the boss and then they have links to Allakhazam, thottbot and other sites that have nice loot tables (allakhazam does a great job im just no good at navigating their site so i just go from wowwiki to it)

If you want a mod that will show you in game go to 
http://www.curse-gaming.com and they have a great add on section