Gallery and Coppermine are pretty widely used by photographer and are free.
Gallery 2 is pretty easy to setup as long as you have a server with the proper settings and FTP access. If you have shell access it's even easier.
Upload the zip file, unzip it on the server via shell commands, and run the installation program from a browser.
There is a step to upload a text file with a confirmation number to your server via FTP to make sure you have access to the server you are installing to.
You will need to provider your MySQL username and password.
It has lots of upload options for images, such as processing a folder and can interface with various programs, such as picasa.
I've installed it a couple of times.
http://gallery.menalto.com/