Join.me is a great new application from the folks at LogMeIn for screen sharing. If you're working on a project and you need to collaborate on a document, or if you want to do a presentation over the web, this is a VERY easy to use product. The free version has a lot of features and its probably all you need to get started.
Starting a screen sharing session is simple. You'll get a 9 digit code that you can email to your participants, and you'll be connected almost instantly. There's also a free conference line you can use for your meeting (its not a toll-free number, but there is no extra charge for the conference connection). You can also communicate by chat.
I installed Join.me recently to test it was was amazed at how simple it is. If you want to get the "pro" features - meeting scheduler, custom link, meeting lock out, the cost is $29.95/month - still a very good deal.
Developing technology that's easy to use is actually very difficult, and Join.me is impressive - give it a try!