Particularly useful when traipsing through (inherited) project-less sites with embedded C# (no code-behind)...
For remote debugging of managed code
aspnet_wp.exe - XP
w3pw.exe - Vista / 2k3+
(Note that msvsmon.exe must be running on remote machine)
And for the JS attach to the client process (say IE) (especially when you cannot use something like FireBug because corp. only wants to support IE).