SoS : http://diablo3blog.blogspot.com/

ACT I
2156 XP - Plague Carrier
2300 XP - Skeleton
2875 XP - Risen, Walking Corpse, Ravenous Dead, Blood Clan Warrior
3594 XP - Servant of Jondar, Hungry Corpse, Highland Walker
5750 XP - Savage Beast
Butcher gave around 57,000 XP.

ACT II
3600 XP - Betrayed, Sand Wasp, Dune Thresher, Fallen, Cultist, Fallen Peon, Writhing Deceiver, Accursed, Vile Swarm
3960 XP - Serpent Magus
4500 XP - Fallen Master
5400 XP - Lacuni Slasher, Pain Monger
The whole Belial encounter earned me around 111,000 XP. Kulle encounter was 54,000 XP.

ACT III
3375 XP – Demon Trooper, Fallen Mongrel, Dark Skeletal Bowman, Skeletal Marauder, Icy Quillback
4500 XP – Fallen Prophet, Fallen Grunt, Soul Ripper, Swift Skull Cleaver, Blood Clan Warrior, Blood Clan Spearman, Reviled, Fallen Soldier, Stygian Crawler, Succubus, Blazing Ghoul, Tormented Stinger, Phasebeast, Winged Molok, Blood Clan Occultist
5625 XP – Fallen Overlord
6750 XP – Herald of Pestilence, Demonic Tremor, Demonic Serpent
11250 XP – Bloated Malachor
Ghom 90,000 XP. Siegebreaker 4,500 XP. Cydaea 112,500 XP. Azmodan (no adds) 90,000 XP

ACT IV
Mobs have the same level as in Act III.
Iskatu 45,000 XP. Rakanoth 135,000 XP. Diablo 22,500 XP, each Shadow clone 4500 XP.
Each Champion gives 3x XP. The main guy (yellow) from rare pack gives 3x XP