Omegle and chatroulette both have "random" chat features, tinychat also has a free video chat...those don't require software installation.
(warning: omegle / chatroulette you may be...shocked...from what you might find).
If you want a video chat specifically to communicate with friends and family, tinychat is probably the best one.
you can use msn. its like skype but its more chat instead of video. if you and who you are talking to both have cameras, then you can use it for chat.
you can also go on webcam on Facebook, I think you just need to add the Video Chat Rounds app - [link removed]