Here is a random selection of links on Expression, mainly WPF/E that I collected after the 4 December announcements.
James Clarke's Weblog Great series on 4 December announcements
TheWPFBlog Designer at Frog Design
Mike Harsh's Blog Mike is a program manager for WPF and has a great blog on the technologies.
Embedding video in your blog using WPF/E Chandra Thota is another program manager here at MS.
Twelve videos in WPF/E Mike Taulty another Microsoftie showing an experiment running 12 videos at once in WPF/E
A number of other links can be found on Wikipedia here.
For developers, there are a number of links that you could check out:
Unfortunately there isn't much out there by designers for designers. Let me know if you see anything.