The closest thing to watching Yo!MTV Raps online is by going to these two places.
This is undoubtedly one of my favourite sites on the web. The site comes with a barrage of rare Ol' Skool clips of all the greats from Big Daddy Kane to Erick Sermon & Onyx! I have spent hours on this site, I hope you appreciate it as much as me.
This website is much the same formate as the one above, just not as slick. It contains a large amount of valuable Yo! MTV raps clips.