jQuery is one of the widely used cross browser Javascript library. One popular platform where you can find jQuery is WordPress. However some people may not be comfortable using jQuery, most probably for its size and its XML usage. So if you are looking some good jQuery alternatives, here are the ones.
DHTML eXtensions
http://dhtmlx.com/The Russian based company that develops the finest of WEB UI components. The Standard version is under the GPL license, you can get it for free, but the Enterprise version needs to be purchased for 900 USD. Click here to check out DHTML
Dojo
http://dojotoolkit.org/Yet another open source with good set of features. Compared to DHTMLX Dojo has better visual effects and animation support. Click here to check out Dojo.
Google Web Toolkit
http://code.google.com/webtoolkit/download.htmlCommonly known as GWT, this is my favorite library. In the point of view of a Blogger, GWT is something that can give you the same performance as in jQuery but remember its light-weighted. Click here to check out Google Web Tool kit.