I only know of three:
www.livemeeting.comwww.webex.comwww.gotomeeting.comOf these three, I prefer Live meeting (although it was even better when it was Placeware - before MS bought them).
On average I use Livemeeting around 4 times a week, and have found they are the least "laggy" of the bunch. You can upload your slides, or show live from your desktop. They also offer the ability to get live feedback from the group, and to accept questions by text. Plus, you can give sharing to one of the other attendees if you choose.
For a new business, it might be better to go with Gotomeeting, as they are (or were) somewhat cheaper, and I don't believe they force you to sign a contract. Either way, that gives you a place to start looking.
None of these will really allow you to videoconference, but for training purposes I think they are quite good.