Here's one my friend wrote, we're using it for in-place editing of html files stored on S3: <a href="http://github.com/micha/jquery-eip/tree/master" rel="nofollow">http://github.com/micha/jquery-eip/tree/master</a>
I used this one on a small project and it worked well:<p><a href="http://code.google.com/p/jquery-in-place-editor/" rel="nofollow">http://code.google.com/p/jquery-in-place-editor/</a>
<a href="http://www.appelsiini.net/projects/jeditable" rel="nofollow">http://www.appelsiini.net/projects/jeditable</a><p>used it several times... excellent; flexible.
This is the sort of thing I'd be wary of using jQuery for. An activity like this demands high performance and the cruft added by jQuery is noticeable in tools like these that I've tested. contentEditable (and its IE relatives) is pretty easy to get the hang of, why not just write one in straight JS?