I just posted about Zero Gravity, courtesy of Tim Heuer's blog post. It's an addicting little game that makes great use of the Silverlight platform. I lauded it as the first game I'd seen (besides Sprawl, which is one of our internal samples) on the platform.
There's more, though. Seems I've been asleep at the casual gaming switch. Check out:
And more. Chris Bowen posts: "Index of Silverlight Games, Most with Source".