Back to the original question....
Items that are located in the "Open with
" slide menu are located in HKEY_CLASSES_ROOT\*\OpenWithList in the registry. Deleting items off this list should only be done if an "Open with
" extension has been wrongly associated with a certain program. Once deleted, you will be free to re-associate it, or just leave it as is. This should not be confused with
Anything found below "Open With
" to the next separator is found in this key in the registry: HKEY_CLASSES_ROOT\*\shellex\ContextMenu\Handlers. In the image example, "The Cleaner", "WinRar", "WinZip" and "Yahoo Email" are the items that can be removed. As a side note, the WinRar and WinZip menus can be useful if you start using them, so it may be suggested that those two entries be left.
Here are other locations for any global entries that only appear after right clicking on certain files or folders:
These are for the items that appear when right clicking on a folder:
These are for the items that appear when right clicking on a drive (hard drive, CD drive, etc):
These are for the items that appear when right clicking on a file. Note that extension specific menu entries are not located here.
There are two ways to approach editing out context menu items. The first is if you don't know what it is, leave it alone. The second is backup the registry entry, try removing the entry and if it doesn't end up being a desirable result, restore the entry you backed up. The good thing about fooling around with these menu item tweaks is that they do not require a reboot to be applied.