Process Explorer, available from http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx, is a brilliant replacement for Windows Task Manager.  The utility provides a customisable top/prstat-like view on the system and is able to give good breakdowns on CPU and IO usage

The default column layout is rather limited, but it’s quick and easy to configure all of the relevant information.  The only thing that does seem to be missing is a pure thread view (as opposed to processes)

Now I’m looking for a decent replacement for iostat and lockstat.  Process Monitor (from http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx) provides a workable replacement for truss/strace… the drill-down features seem reasonably good, although the interface is rather clunky for initial investigations