Hi,
Following this question from last year. I am checking two open source ribbon controls:
Do you have any experience (good or bad) with any of them? or perhaps know of another open source ribbon control?
there is one included in the WPF toolkit dont know how good/bad it it. we use one that we bought.
I've been trialling the WPF toolkit. Bear in mind - it's not open source per se - you don't get the source code. However, I believe it is free for use etc.
It's reasonably easy to use and has some reasonable commanding support. The documentation is not particularly in-depth, but it looks good - same as the ribbon used in Office 2007 etc. and has a few themes.
I'd say give it a look before spending money on a third party commercial ribbon control.