Libraries I used:

• jQuery (hosted by Google)
• markItUp – textarea replacement with added buttons for easier typing of markdown/textile/bbcode/html syntax. Uses jQuery. Used on this blog.

Libraries that look useful for the future:

• SoundManager2 (GitHub repo) – playing audio
• CodeMirror (GitHub repo) – textarea replacement for editing code, has syntax highlighting
• WMD – a markdown plain text editor, with live preview implemented in JavaScript, used by StackOverflow

Other lists:

• templating languages in pure JavaScript