Did you get in trouble finding elements through OOB features with hundreds (or thousands) of hundreds of documents/pages? I think this is something everybody meet sooner or later in a SharePoint environment.
I have several opportunities to improve Asset Picker, but the way it is built (based on a Browse & Find instead of Search concept) it was really difficult to hack it and make it globally available.
At the end we got to a scenario with too many custom development to be able to accomplish this solution.
So, did I find any other suggestion to improve authoring/editing experience?
Been able to Search for content inside MOSS/WSS without moving through several windows, and using search built-in capabilities, just right where you are editing.
A Feature deployed through a Solution package, that contains a delegate control begin included in the Additional Page Header. This control manage a modal css window, that allows the user to search and filter results from a form control.
Options for the "client engine" would be:
Personally, I would choose JQuery (even before it was going to be included in VS :))