ExtJS vs. JQuery
jQuery UI has a bunch of controls, but you would probably need to extend out to other plugins depending on the situation.
Im on the jquery evangelism team as well as a speaker at the upcoming Extjs conference. We use ExtJS extensively at Marketo.
If your requirements are simple, publically accessible, and being done by web developers, then use jQuery.
If this is a more complex situation, you have more hard core engineers, behind a username/password, then I suggest ExtJS.
ExtJS is a lifesaver for our flagship product and we clearly fall into the latter camp. However, for our public website, We use jQuery because its more lightweight and easier.
Any comments on the levels of support from any of these libraries? (From the community in the case of jQuery UI and Sencha in the case of the commercially licensed library.)
Ive tried dojo. Its complicated like extjs, but without all the great components. Regarding support, both have been very good. The Jquery community is stellar, plus stack overflow works great as a fallback.