A new product I've been using recently to provide remote support is called Crossloop. It's a bare-bones simple remote assistance application that allows you to see and help users remotly. The technology is based on VNC. It works well and it allows easy remote control and assistance without those pesky firewall issues.
I've been using Crossloop for remote support but it also works well for remote presentations. While services like WebEx provide many more features in the years I've used WebEx I've never seen any of those features actually used. Like it's expensive counterpart Crossloop allows you to view/share a monitor remotly only it allows you to do it for free. Crossloop is limited in that it only allows one-to-one connections. You can't do a one-to-many. However for most of my client-consultant meetings this is perfect.
Getting custoemrs to install Crossloop and call me up is easy and allows me to solve problems faster with less back and forth with the customer.
Overall I like it. It's not as polished as Fog Creek's Copilot for support isues but Crossloop is free to use and can be used beyond support. Check it out at Crossloop.com