Basically, I'd like to select some text in Notepad, Word, my RSS reader, what-have-you, and be able to lookup that phrase in Google. Are there any utilities that allow me to do that?

A context menu would be difficult as they are generated by the application rather than the operating system.

However, you can use a simple AutoHotKey script to give you a keyboard shortcut instead. The script below should work in any situation where you can use Ctrl + c to copy to the clipboard.

#s::
MyClip := ClipboardAll
clipboard = ; empty the clipboard
Send, ^c
ClipWait