Photo gallery

I need to find some photo gallery software for a web site.

Here's are my two major requirements:

-- instead of having separate albums, I want everything in one big album with the ability to tag each photo with keywords. Then I can display a list of keywords instead of albums, and clicking on a keyword will bring up all the photos that match. Kinda like Flickr without all the special effects, or Photoshop Album (but for a web site).

-- I want other people to be able to upload photos, but not have them go to a live directory and not have them be tagged. I want to handle tagging the photos and making them live.

Any ideas?