When I was searching for a plain and simple gallery script a while back, I stumbled upon minishowcase, a beautiful little gallery script, written in php with Lightboxfor the required eye-candy. Minishowcase has just received a major update - several things that were on the 'to do list' of the author are now actually implemented. I just installed it and was amazed : Performance has suddenly gone up 200% ! Where the script loaded slowly before, it now loads quicker than you would actually believe.
One of the major qualities of minishowcase is low-configuration. There is a configuration script where you can adjust certain settings to your liking, but out of the box it simply runs. You just unpack it, create your directories where the images will go and you're done. Really, that's it. For all of you that host their own stuff - I can recommend it.