The latest is Resource Monitor, which was in Vista and Server 2008 but is all tarted up in 7. This is essentially a beefed up version of Task Manager and gives you the kind of information you could get in previous versions of Windows only by installing lots of Sysinternals applications and really having a good idea how to use them.
It can be launched within Task Manager (presumably to wean people off this phenomenally old but still reassuring bit of Windows - I have to say I like the fact that Task Manager is still there and looks the same as it did 15 years ago. It makes you think that under Windows 7 is NT4 trying to get out) by clicking the Performance tab and then the really obvious button at the bottom of the resulting screen.
Or Click start and start typing "resource monitor" into the search bar. That works too.
What you get is a bit like Task Manager but with disk and network traffic too. Its a very good place to troubleshoot bottlenecks on a system that is running Windows 7 slowly as it can be fired up so fast to see graphs for CPU, Disk, Network and RAM. These four sections can be expanded to show the processes using the most of that resource, which in the case of Disk especially was information that was previously not so easy to come by.
The Vista one is all well and good but lacks a lot of the detail and is less customisable. And its less cool, because its in Vista, and everyone knows Vista is rubbish.
Sorry, I didn't mean to let that out.