What new NPCs are available in 1.2?

According to this wiki and this wiki:

Dye Trader will move in when:

• Any material used to make dye is in the player's inventory, such as the yellow marigold.

Party Girl will move in when:

• You have at least 8 NPCs (Note: There is a 2% chance for the Party girl to spawn each morning, so it can take a while for her to arrive.)

Steampunker will move in when:

• The player has killed any Hard Mode boss and there is a suitable house for her.

Painter will move in when:

• The player has obtained at least 4 NPCs.

Witch Doctor will move in when:

• The player kills The Queen Bee.

Pirate will move in when:

• The player fights the pirates by using a treasure map obtained by killing hard-mode sea monsters.

Cyborg will move in when:

• The player kills Plantera.

Truffle will move in when:

• The player has a house with Mushroom Furniture (Mushroom Workbench/Mushroom Doors/Mushroom Chair) in a surface Mushroom Biome.

Note: Just like with any NPC, the player must have an empty and valid house available.