JAlbum is one of the very best web photo album creator programs. Version 7 was just released (history) and has some major improvements to the user interface, which is packed with options.
I've used JAlbum in the past and it's a great program with tons of different web skins that effect how your photo album looks and behaves.
Some people prefer server-based photo album software, for which there are also some good free scripts (Gallery is the big kid on the block here). But many people prefer to have the pages generated on their local pc and then uploaded. JAlbum is like that. All pages are generated statically for you and you just upload the results (or let the program upload them for you).
ps. It's called JAlbum because it's written in Java - works on windows/mac/*nix.