I found some really interesting articles on the new ASPNETResources.com site, including stuff on Doctypes which was pretty good and tips on getting CSS2 Intellisense support in VS.NET - worth keeping an eye on how this site develops methinks! Also a particularly interesting blog on the site covering similar subjects...
UPDATE: Poking around some more, just noticed they have a really great article on XHTML support using Response Filters in ASP.NET - excellent coverage!