How to copy file path to clipboard?

Beginning with Vista you can just Shift+Right click on the file in Explorer and select "Copy as path":

        

This even works for multiple files, which are put into the clipboard one per line.

In Windows 8 this is exposed in the Explorer ribbon:

        

Use CopyFilenames

or

Copy Filenames to Clipboard Utility

Windows XP has no way to copy a list of filenames to the clipboard (this has changed in later versions of Windows, starting with Vista). A Microsoft Knowledge Base article suggests writing a small *.bat file that runs the DIR command, collects its output into a file, prints that file, then deletes it. This may be convenient some times, but it would be more useful to be able to select a list of files, and have the names of them put on the clipboard. Then you could paste them wherever you needed them.

So here's a utility to do that. You have to do a bit of work yourself - but not much - to install it. Here are the instructions:

1. Download the executable. It's only 20 KB, so it should take only seconds even if you're using dial-up access. Save it wherever you want it to reside on your system.

2. Create a Shortcut in "Go To"

   1. Go to the "Send To" folder under your name in \Windows\Profiles in Windows Explorer (or maybe XP Home puts that directory under the Settings folder, I can't remember).
   2. Right-click in the right-hand pane, where the filenames are. Select "New|Shortcut".
   3. The "Create Shortcut" wizard will appear. On the first page, type in the path to the executable, or use the "Browse..." button to find it. Click ""Next".
   4. On the second page, type in a name for your new menu option. I used "File Names to Clipboard", but pick whatever will be meaningful to you. Click "Finish"

That's it; you've got it installed. Now select one or more files, right-click, and move your mouse pointer to "Send To". A submenu will appear which will include your new command. Choose that command, and a list of the files you've selected, sorted in ascending order, will be on the clipboard.

Source: http://members.cox.net/slatteryt/FNtoClip.html

I use the MS 'Send to X' PowerToy available as part of the Windows 95 PowerToys set (MS download link).
This adds 'Clipboard as Name' (as well as 'Clipboard as Contents' and a few other options) to the right-click 'Send To' menu.
The easiest way to install is to extract the downloaded W95powertoy.exe with a Zip utility, rightclick 'SENDTOX.INF' and select 'Install'. You can remove any unwanted items from the 'Send To' menu by opening it in Explorer.

Works fine on Windows XP - not on Windows 7, but as noted by Johannes, you can use 'Shift + right-click' instead.