This is the best gallery plugin.

Extremely lightweight, it does what you want and doesn’t waste any resources while doing it. And, unlike some of the more popular overblown gallery plugins, it doesn’t try to transport visitors into a new dimension of reality when all they want to do is look at a picture.

My only issue is that the latest update added a feature to the image captions that requires editing the plugin’s code to deactivate – I’d much prefer an admin page for that. But, I suppose it’s all in the name of being lightweight!