I already have a YouTube account and my favourites include: early tv performances by a variety of musicians; a great rendition of 'Mr Bojangles' by Sammy Davis Jr; amazing live duet between Stevie Wonder and Ray Charles performing Stevie's 'Living in the City'; Stevie doing the awesome 'Superstition' on Sesame Street; the Jacksons doing 'Dancing Machine' and 'Shake Your Body Down (to the Ground)' [Jimmy Saville used to give you extra points for getting the brackets right in song-titles...!]; Bill Hicks; funny Fry and Laurie skits; nerds talking about comics; episodes of The Actors' Studio.... and much much more!
A great discovery was finding lots of excellent philosophy content: I was really happy to see that someone had uploaded episodes of Bryan Magee's 80's television series, interviewing eminent contemporary philosophers, which was hugely inspiring to me at the time; the sort of simple 'talking-heads' tv that's unfashionable these days; there are also fascinating filmed discussions or lectures by the top philosophers in the field: Davidson, McDowell, Rorty, Searle... It's always interesting to see philosophers whose work you've read intensively talking more informally and discussing differences with each other. What I find most striking is how hard even 'the great and the good' find it to makes themselves understood to each other - a frustration I've always found characterises philosophical discussion and used to attribute to my mediocrity.
It goes without saying, you definitely need to sort the wheat from the chaff with YouTube. You can search, e.g., for philosophy topics and find lots of youthful amateurs rambling on in their dorm-room. However, occasionally you find someone with a great archive.
Reading comments on YouTube falls into the category of 'life's too short' most of the time. Contributors are almost invariably given to banality, horrendous abuse or eye-rolling panegyric. (I am myself a shameless kiss-ass on the blogs of artists I admire. You get the feeling that critique is a breach of etiquette: the familiar bidding that, 'if you have nothing nice to say, say nothing', seems to apply even more strongly in the case of blog-commenting)