As sad as it sounds we're currently using Skype's screen sharing (single person) and voice conferencing with Google Draw at the moment. Will try connectnow.acrobat.com as it looks decent.
oops - the title really should be "Ask HN: What's your favorite free web conferencing tool?" I thought HN would add the "Ask HN" part for me, and now it's too late to edit the title. Anyway, thanks for the replies so far.