I'm looking for an easy to use wireframing tool. I've heard of gliffy, are there any others?
Specifically, I'd like something that is
You could just wireframe in HTML.
Seriously, don't ignore the advantages of what straight HTML wireframing can offer to the process or what tools there are to make it easier and effective. Things like jquery and polypage make HTML a very powerful and capable wireframing and prototyping tool.
I wrote a blog post a while ago that explains some of the advantages and tools of straight HTML wireframing (sorry for the gratuitious self promotion).
Another great website wireframe/mockup tool is Mockingbird ... it's collaborative and does decent export.