Gallery has long been my only answer if someone asked for an image gallery. It has pretty much all the features you could ask for:
- doesn't need a database (makes it very easy to backup as well -- just tar the entire directory)
- makes nice URLs using mod_rewrite
- generates thumbnails in multiple sizes
- has a built-in permissions system for protecting albums
- slide show mode, which goes throw all the photos in an album, cross-fading the images
- easy, web-based install
- supports commenting of images
- Windows XP web-publishing wizard or stand-alone Java-based, cross-platform Gallery Remote app
Pretty much the only downsides to Gallery are that the HTML is a little crufty and hard-coded into the app, making it a little harder to customize. As well, not being based on a database, some more advanced display/sorting features aren’t available. One gotcha with the install is that Gallery cannot run with PHP safe mode turned on, which is a problem with some shared hosting environments.
Gallery 2.0 is going to use a database and be re-written to separate content from presentation.