Another tool I made for my game engine (Oh I do like making tools!), the SpriteSheet creator takes an input of as many files as you want and generates a sprite sheet (One image after another) for all the images. It has a few features, not much compared to other tools out there, but I didn't need all the stuff the other tools had! Download with source

Features:

Sprite sheet generation (Duh!)
Offset support
Custom row and column image split up support
Background colour support
Image scaling