I just started using Convoq ASAP for demos, meetings, and troubleshooting at work. Convoq is a web-based conferencing system, much like Macromedia Breeze or WebEx. However, it is entirely Flash-based and only $50 a year for meetings of up to 5 people. This is a lot cheaper than any of the other services available right now.

Convoq works with any IM client you have on your machine as the basis for your contact lists. It also allows audio/video conferencing, screen sharing, and uploading of PowerPoint presentations.