The SysInternals tools -- including Process Explorer, Regmon, Filemon, and many more -- are now available here on microsoft.com.  A couple of major highlights include Process Monitor, a new tool that supersedes Regmon and Filemon, and the SysInternals Suite, which combines the whole set of SysInternals tools into a single download package.

In addition, check out Mark's new TechNet blog, and the SysInternals blog.

URLs:
http://www.microsoft.com/technet/sysinternals/default.mspx
http://blogs.technet.com/MarkRussinovich/
http://blogs.technet.com/sysinternals/