If you're looking for the highest rated look no further than the Top 10 Webcast page:
"Fast and easy access to on-demand webcasts – what could be better? After selecting your webcast, simply enter your name, e-mail address, and company name to start watching, or you can download the webcasts to view when you’re offline. We’ve selected the 10 highest-rated Microsoft webcasts, as chosen by customers like you. And, as always, these webcasts are free.
"For a richer experience, make sure you’ve first downloaded the Microsoft Office Live Meeting 2005 Replay Wrapper. It allows you to explore webcasts and complete the evaluations, and it's something you only have to do once."
Bonus: If you're a US or Canadian resident, watch one Top 10 webcast by June 30 and you'll get a chance to win a Palm Treo smart phone (click here for official rules).
No surprise that the MSDN Webcast on "MechCommander 2 Mods" is among the top ten. ; )
And you can enter to win Gigabyte Creative Zen Media Player when youcomplete and submit an evaluation form following a live or on-demand Microsoft Webcast in the Webcast Series. That includes webcasts on TechNet, MSDN, Small Business, Microsoft Business Solutions, Microsoft Office System, Microsoft Executive Circle, Momentum and Security. (See official rules for more details.)