Happy new year,
I've released a public beta of a YAML editor I've been developing. I'm looking for feedback from the YAML community. Its available at http://www.codeplex.com/yaml, there are a couple of screen shots there to give you an idea what it's like.
The editor is built on top of Visual Studio. Currently, a copy of Visual Studio is a pre-requsite, but I'm planning to take advantage of a redistributable package from Microsoft that will allow it to run without purchasing Visual Studio. I've not done the integration work yet for a setup bootstrapper to integrate the two.
Current features include syntax based coloring, brace matching and a limited set of on-the-fly syntax error messages. Please report any problems you might find using the issue tracking system on that web site.