Synchtube is a great free service for watching videos. It allows users ,beside watching their favourite videos, to chat and talk about their videos in real time. It provides a social video watching experience. Synchtube supports a wide spectrum of media types. It initially started with just YouTube videos and expanded to include : Vimeo, Dailymotion, Blip.tv, Soundcloud, Ustream, Justin.tv, Twitch.tv, Livestream, Slideshare, and Imgur.
Synchtube allows users to synchronise different types of media across the web. They can also create instant rooms, invite friends, watch videos, listen to music, share documents in real time. This is all for free. You just need to register.