Here are two links to videos on Unsupervised Learning of natural language syntax.
Chris Manning gave this talk at MLCS 2007. It is a fairly detailed discussion of the work that Chris did with Dan Klein on learning syntax structure. Dan used the material for his dissertation.
Dan Klein gave this talk at UAI 2008. It is more high level, and describes how Dan and his students have applied their work to a few other areas of unsupervised learning.
Both these videos are worth watching.