Diablo 3 Walkthrough Part 36: End of Act I

After killing the Butcher, you will receive the following achievement:

Butchered!
Kill the Butcher on Normal Difficulty

Also, you will probably get the following achievements at this point, if you explored everything:

Beastmaster of Tristram
Read the following Bestiary Lore Books in Act I:
Beast, Dark Berserker, Carrion Bat, Carrion Nest, Imp, Dark Cultist, Ghost, Ghoul, Grotesque, Hellion, Khazra Shaman, Quill Fiend, Scavenger, Skeleton, Spiderling, Spider, Treasure Goblin, Unburied, Dark Vessel, Withermoth, Wood Wraith, Wretched Mother, Risen Dead, The Spider Queen, Butcher

There Will Definitely be Blood
Explore the following areas of the Halls of Agony: Halls of Agony Level 1, Halls of Agony Level 2, Highlands Passage, The Cursed Hold, Halls of Agony Level 3, Chamber of Suffering

Be sure to collect all the loot that dropped on the ground. There will be LOTS of gold, magic items, and possibly one or more rare items. Your quest log updates:

The Imprisoned Angel
Find the Stranger

Head north through the corridor, and take the exit into the Cells of the Condemned. Go down the stairs, following the trail of blood. You see cultists, members of the coven, conducting a some sort of ritual on the stranger. You will be attacked by Dark Ritualists, Dark Berserkers, Dark Cultists, and Dark Wizards. Kill the cultists surrounding the Stranger. Then, talk to the Stranger. He tells you he is dying. You give him his sword. He remembers now, his name is Tyrael. He was an archangel of the High Heavens. He was the embodiment of justice.

This completes the quest, The Imprisoned Angel. Talk to Tyrael in the Condemned Cells. He remembers the warning he came to deliver. Belial and Azmodan, the last Lords of Hell, are unleashing a tide of darkness that will drown this world. Already, Belial's shadow has fallen upon Caldeum. We must move quickly. Let us return to Tristram to make ready.

Return to New Tristram
Talk to Tyrael in New Tristram

Tyrael opens a portal to New Tristram. Follow him in, then talk to him in town. He tells you that time grows short. Belial's influence is spreading through Caldeum. He believes Maghda and her coven will lead us straight to Belial. Leah does not want to go anywhere until her uncle Deckard has been laid to rest. So she will not join you as a follower.

Tyrael tells you that he has called for a caravan to guide you to the east. Speak to the caravan master when you are ready to go. We will see to Cain as soon as we depart. Your next objective is to talk to the Caravan Leader, who is standing nearby. You should finish any exploring or other unfinished business around New Tristram before leaving. Your followers (Templar and Scoundrel), and Blacksmith travel with you. It will ask you "Do you wish to travel to the next act?". Once you are ready to depart, speak with the Caravan Leader and choose to proceed to the next act.

This concludes Act I of Diablo 3.