(E)2: Photo Gallery With MooTools
By default, (E)2 has 4 themes which can be switched-between easily. It has an auto-loading thumbnail viewer which can be hidden too.
This photo gallery requires PHP to run and does not need any database.
In the near future (E)2 gallery will have a "pro" version with more features and you will be informed of it via WebresoucesDepot for sure.