I quite like Kimdaba, now known as KPhotoAlbum. In particular, it allows you to tag images with multiple tags, and you can view your pictures by date or tag or group (a superset of tags). It will export to HTML, but the version I used would set up gallery thumbnail images in a grid on a selected screen size. I think that the gallery should wrap to fit the current viewing size, and not assume the user is browsing full-screen at a particular resolution.
Kimdaba does nothing with your files on disc, but instead catalogues them in an XML index file, which also contains the tags and other information for each image. It also plays nicely with Kipi (the KDE Image Plug-ins) for handy dandy image fiddling. It's certainly worth a look. A
