Saw this question here : What Great .NET Developers Ought To Know (More .NET Interview Questions)
It will show processes that have loaded modules (usaully .DLL files) hosting the .NET runtime. The same technique can be used to search for other DLLs that have been loaded.
On a related note, Process Explorer is a Microsoft task manager replacement that will show .NET processes highlighted. I cannot recommend it enough. It is well worth investigating along with the rest of the Sysinternals Suite.
This is a very useful command line tool in windows that shows you a list of all running processes. Passing in a command line parameter of /m "mscor*" lists out all of the processes running on your machine running that are using assemblies that begin with the name "mscor". The "*" is a wildcard character.
It would seem to list all processes using modules like mscoree.dll, mscorwks.dll, etc. This would be .NET processes and possibly processes hosting .NET plug-ins.