Minecraft mod that helps with the first night
Mob Blocker adds a mob-blocking block: the Chunk Protector. This block will, for 3 (configurable) days, protect the entire chunk it is placed in from all types of hostile mobs. Upon first entering a world, each player is gifted one of these blocks to use. It's recommended that they use it to assemble shelter at night while shielded from danger. After the Chunk Protector decays, you'd better have a wall up!
Also available is the Area Protector, which can be crafted, but only protects an 11*11*11 area by default.
This mod is very configurable, allowing you to change most of the important settings so that you can tweak the mod for your playstyle.