RobotC is running some nice, completely free, online classes to teach the basics of using their language with the NXT, Vex, and FTC. The NXT webinar is held on Tuesdays from 7 to 7:30 PM EST. You can see and register for it here. There's only one Webinar left for the NXT, but you can watch recordings of the previous three Webinars on the above link as well.
I haven't seen the NXT webinars, but the FTC webinar is taught by Timothy Friez, one of the developers for RobotC, so they seem to have the experts teaching these courses. Not only do the webinars provide nice learning sessions, but also give you a chance to ask questions. Definitely something to take a look at if you want to switch to a more advanced language than NXT-G!