My jLINQ plugin is a jQuery version of .NET LINQ. It's made for working with in-memory collections (not talking directly to the server) and let's you use syntax similar to the following.
var results = $.from(data)
.ignoreCase()
.startsWith("firstName","m")
.or("n")
.isNot("administrator")
.orderBy("lastName")
.select();
It supports a bunch of other commands that you find in LINQ for ordering and grouping along with most of the selection commands like contains, between, greaterThan, etc...
I always use Facebox to display pop-up forms and messages to the user. It keeps the UI clean (most of our users use Facebook), and yet it's not as bland as using alert().
[edit] - Recently I've been using JQuery Tools as an alternative to JQueryUI, JQuery Tools is more HTML5/CSS3 centric: http://flowplayer.org/tools/index.html