Free Web Conferencing at Vyew.com is a multifunctional workspace collaboration platform. You can hold webinars, with a conference call in number and have presentations Free accounts are limited to 20 participants.
Dim Dim is a webinar platform avialable for free. You're limited to 20 participants in the free account.
YuuGuu is completely free and supports cross platforms. It allows you to host webinars and share screens. It's easy to use.