Slap Happy, a series on lesser-known silent comedy shorts, is availabe on DVD. Vol. 1 is deeply discounted, so you can sample the series. I didn't see any of the half-hour episodes when they aired on PBS, but they are well-reviewed, and are said to focus more on lengthy clips from the movies, rather than long commentaries and talking heads.

Speaking of documentaries, I don't believe I mentioned yet that F For Fake came out on DVD this week. I snapped mine up on Amazon, and am planning on devouring it this weekend (it's a two-disc Criterion Edition, so it's got a lot of extras). I'll give you my verdict once I've watched it.