I've created an Ajax Filterable Palette and checked the code in via svn and also created a JIRA (https://issues.apache.org/jira/browse/WICKET-3113) with a quickstart and the patch file.
I created this component because I needed this functionality and could not find it anywhere nor could I find anyone with the solution. Please look this component over and if necessary let me know of any changes that need to be made or feel free to make changes yourself. I think this would be a valuable component to wicket and it's users. Thanks, Geoff Lancaster
