PixVue is a metadata editor. I found it while searching through dpreview.
It wedges into the right-click menu in the Windows file explorer. From there, you can edit metadata and manage PixVue.
It updates IPTC/XMP data directly. I like this feature. It avoids yet another program-specific database, the usual interoperability problems, and the associated backflips in the workflow.
It also adds a 'My Gallery', where you can drag and drop selected files into virtual folders. I haven't played with this feature, but it looks interesting.
I ran across a few display quirks when updating the explorer window, but this are minor annoyances when compared to how easy it becomes to update image metadata.
You might want to give it a try if you want/need to manage your metadata, particularly keywords.