Cheap, easy and pretty good is to split your solution into audio and video parts. Skype does really well at audio. For video, you could use an ip camera and a browser or bolt in anything else you like.
If you want completely non-proprietary, ekiga is pretty good in its latest incarnation, though to get good video you have to use the non-free h.264 and for many-to-many you'd have to set up a sip router. That ends up harder.