One of the best kept secrets in the field of web design seems to be that all the really clever stuff you see on web sites, typically is done by someone other than the website designer. Historically I've made extensive use of ThemeForest.net for Wordpress templates, but for more interesting online applications, they have a sister site called CodeCanyon.net. In particular the Javascript section has some real gems for the price of a sandwich that can be easily worked into one's online application. These are a few I've been making use of recently;

Pull Out content Panel

This has a really nice slide in effect, but also a really nice built in content scrollbar. I've been using it as a Dashboard widget palette, looks really nice and it's operation is pretty smooth.

NinjaRadial

Something that hadn't occurred to me previously, but context menus in Javascript are notoriously unsatisfactory so an alternative is most welcome. I think this draws on experiences from the computer gaming community, but either way it looks really cool and it's quite nice to use.

Slick Modal

I spent quite some time playing with different Javascript popups / Modal plugins, and there are some quite nice ones out there. I finally settled on this one, although I still need to change the colours, it's got a whole bunch of whizzy effects, and it's quick.

These are all sub-$10, that said there's a whole lot more completely free code kicking around, and while some is of very questionable quality, there are some other Widgets that are as good or better than the commercial options. I'm using something called Gridster for my Dashboard, unfortunately it looks like the sponsoring company has been bought, but what's there now is still very good. It supports drag and drop re-ordering, widget resize, dynamically add and remove widgets, has load / save facilities etc etc ...

Last but not least, a Widget I've been playing with off and on for quite some time is jsPanels. Now jsPanels is a hugely underrated / largely unknown project designed to allow "windows" style panels to be utilised inside web based applications. I spent a little time last year working with the author to enhance some of the features available and it's an incredibly powerful bit of code, so watch this space for more in the future. Currently I'm using it for displaying online users, but there's far more to come.

The dynamic nature of the panel makes it very easy to update, and the "minimise" option still allows you access to the title bar for updates, and you have a good dynamic resize tag in the corner. But the best features is the load/save functionality. The panel can encapsulate javascript code that is used to generate the content for the panel, then there is some serialisation code to bundle all active panel up into something that can be stored in a server-side database .. so you can run a persistent panel based application almost entirely on content generated callbacks - very flexible and very cool!