The TinyWebGallery is a free php based gallery that is very easy to install, extremely user friendly, does not need a database (uses xml files) but still has all the features you should expect and much more.
Besides the features you find in most other galleries TWG has e.g.

AJAX + Flash navigation with sliding thumbnails
XML based - no database needed
TWG Admin to upload/manage images, manage
users, Color Manager, Configuration of TWG ...
Keyboard navigation (arrow keys)
3 different slideshow types
Protected galleries
Text and image watermarks
Full video support
TWG Flash uploader
Frontend in 24, backend in 5 languages!
Fullscreen mode
Remote picture support
All features can be enabled/disabled/configured
And a lot of things that makes this gallery unique.
Go to the features page for more details.

TWG can be configured very fast for a professional gallery like a model agency but also for the pictures from the last ski holiday! Just check out the demos and the list of all functions. Maybe TWG is the image gallery you where looking for so long!

TWG Flash Uploader Overview

The TWG Flash Uploader is a very comfortable way for your users to upload file to the remote server. Because it's based on flash it can be used by almost everyone. You can simply upload files by selecting files on your hard drive and simply press the upload button. Just select the different demos in the menu to see how it works!

You can manage your files as well. You can e.g. create, rename and delete folders and files, browse directories, edit files and much more.