Sortable Tables for Prototype 
Testing it out, I had a few issues with it — it was quite slow, it required markup that I considered unnecessarily verbose, it relied on a superfluous logging library, and there was some potential for namespace clashes when let loose amongst other JS (
So I ended up borrowing Inigo's useful approach to the problem and rewriting the code mostly from scratch. This implementation resolves the issues listed above and does some caching of comparison data to gain a little speed. Also, it's 4kb. Download it:
Like Inigo's version, this is released under the Creative Commons Attribution-ShareAlike 2.5 license.
Here's a simple demo. Click the headings to re-sort the table:
|1||Thomas Edison||$13.50||13 Feb 2008|
|2||Nikolai Tesla||$21.00||4 Aug 2007|
|3||James Harrison||$13.27||25 Dec 2007|
* Obviously, this may not work within your feed reader.