I'm looking to implement a build system that will run unit tests and JSLint on the Javascript, generate documentation and compress JavaScript and CSS into minified packages.
I might also add an integration step, which automatically uploads the code to a server on each build.
I feel overwhelmed by all the choices in build systems - some targeted toward .NET, others to Java.
What's the best system for my requirement, considering that the choice back-end is irrelevant?
Any build system would work, but there are none specifically designed for it. I would recommend either Ant or NAnt depending on if you're more comfortable with using Java or .NET. Either would work well for your purposes, running command line tools for the actions you want as part of your build.
You can also find 3rd party tasks specific to your tasks to make it easier:
Ant JSLint http://jslint4java.googlecode.com/svn/docs/1.3.1/ant.html
For continuous integration I would recommend TeamCity. It will work well with any build system, provides a great interface, and is free for up to 20 projects.