Top10 Most Useful JavaScripts

What are the most important and useful JavaScripts that no web developer can live without?

And which is the best version of each of them?

This is my attempt to answer those questions and gather the code in one place.

How to tell a good script archive?

Is there a sense of editorial control about the archive? Have the scripts been chosen with care? Are they writtten by one person or submitted by anyone?

Does it have editors or users ratings? Does it allow users to post comments?

Does it list the browser compatibility for the script?

Good JavaScript archives:

The JavaScript libraries that I got these code snippets from, and other useful sites:

http://www.dynamicdrive.com/ - recommended
http://www.hotscripts.com/JavaScript/ - recommended
http://www.brothercake.com/scripts/ - not many scripts available, but still recommended
http://www.scriptsearch.com/JavaScript/Scripts/
http://javascript.internet.com/ - easy to use, but often broken in modern browsers or not Y2K compliant
http://www.designerwiz.com/javascript_cut_paste_code_list.htm - professional stuff, but difficult to navigate site due to barrage of marketing
http://www.mattkruse.com/javascript/ - mix of complete scripts and widgets to include in other scripts
http://www.quirksmode.org/index.html?/js/contents.html - recommended although more theoretical, tries to teach you JavaScript
http://evolt.jeffhowden.com/jeff/code/ - for experienced developers

Poor JavaScript archives:

http://www.astalavista.com/code/javascript/archive/ - One of the top results in google with a good depth of scripts, but can you be sure they are good or not? No editors or users ratings, no browser compatibility data given, and in my tests the scripts rarely worked in anything other than IE.