If you call yourself a Web Developer, you have to visit this site.  Yahoo! User Interface Library is packed with extremely useful set of UI controls that you can download and start using immediately.  And best of all, they are provided under BSD license.  Which means you are free to use them without paying even a cent to anyone as long as you follow what I call no-brainer-rules.  Animation, XMLHttpRequest transaction management, DOM Utility, Drag & Drop, Event Manager, Calendar, Slider, TreeView.  These are all packaged together as a very easy to use library.  Next time you work on a redesign project, you should definitely consider using these.

And if you are having a stupid battle with your product manager about how a certain interface should work, send her a link to Yahoo! Design Pattern Library and go back to coding.  For web application interface stuff, you better listen to Yahoo! engineers.