Lussumo Filebrowser – Now with awesome thumbnailing power A highly optimized filebrowser in PHP that allows simple thumbnailing and viewing of photographs. The DEMO is quite refreshing and it validates XHTML 1.1 Transitional! Though I would suggest better use of HTML lists, this product looks to be truly amazing. Also from Lussomo is Vanilla which is a web forum that Matt mentioned in his recent podcast interview.
Filebrowser is SCREAMING to be integerated into WordPress as a simple, in-post gallery creator that does not break validation. Imagine posts as albums and post categories as album categories. You can even add a random thumbnail from a post as a teaser in the excerpt.