Included in Windows Vista and Windows 7 is a little command line utility called Clip.
It's very simple: it pipes the output of your command to the clipboard.
Here's how you might use it:
c:\Users\Jon>dir | Clip
It can also be used as a command with a file as an argument, to place the contents of the file in the clipboard:
c:\Users\Jon>Clip < foo.txt
Then just ctrl+v to your heart's content.