Windows Live Ideas is a good place to bookmark (you know, that thing you used to do in the 90's with web pages when you wanted to regularly check for updates...). It outlines all of Microsoft's products on the Live platform, most of which are in beta currently.
Given the brand confusion about MSN and Live recently, here is a good definition of Windows Live:
"What is Windows Live?
Your online world gets better when everything works simply and effortlessly together. That's the basic idea behind Windows Live. So the things you care about - your friends, the latest information, your e-mails, powerful search, your PC files, everything Äì comes together in one place. This is a brand new Internet experience designed to put you in control. And this is just the beginning Äì you'll see many more new services in the coming months."