Ask HN: Tools for auto-tagging

I have a bunch of disparate files/items and I need to generate tags for them quickly. I haven't found much in a quick search, and I don't have time to spend. Can anyone recommend an auto-tagging system that's fast to get running?

I don't need it real soon, but I can't spend too much time getting it running. I would expect some of you guys already have something running, and I'd appreciate leveraging your expertise.

Thanks.