Looking for a jQuery MultiSelect Widget that can handle thousands of items.
Really like this: http://www.quasipartikel.at/multiselect/ but the performance on it after a few hundred items is terrible.
If your potential list of items is really long, I'd recommend something like jQuery UI Autocomplete that can use AJAX to send a much smaller subset of items based on key strokes. Here's an example that allows multiple selections: http://jqueryui.com/demos/autocomplete/#multiple-remote
However, you're not going to want to use this to choose "thousands of items". You may argue that you need a control that allows you to click on an item, scroll down a few hundred rows, then Ctrl-click to choose them all. That's where a better design comes in. How are those hundreds of rows related? Can you create a hierarchy of groups to choose from? As I said before, any control you attempt to do this sort of thing with is going to perform horribly.
This widget works surprising well with approx. 5000 items. I tested in FireFox...