Though it cost a few hundred dollars per month, Livestream would provide you with an excellent platform that has no ads. Otherwise, Ustream would be a good option. Justin.TV will bombard you.
Try Veetle.com - you need their plugins, but their video quality is superb and you can stream in HD and you can make your channel 'private'...or pay the money and use Livestream.
Yep Ive used Livestream a bunch. The free version and paid version. Only needed the paid version when receiving commercial from third party companies were not acceptable.