If you want an open-source text editor that has tons of cool features and is easy to learn and customize and you don't mind Java, jEdit is great. In fact, I've been trying for a while to switch from jEdit to Emacs (for various reasons), but if I'm in any kind of a hurry, I keep going back to jEdit because it's so headache-free to use. It's pretty too.
(If you go with jEdit and don't have the necessary runtime environment already, don't use their link to the full development kit. And don't pay any attention to the mess of acronyms (SDK, JDK, J2SE, etc.). The development kit is the runtime environment plus additional stuff (compiler and packages) that you don't need unless you are building Java programs. You only need http://www.java.com/en/download/manual.jsp [Broken], which you likely already have.)
Emacs seems like it can do anything, but it also seems to take a lot of energy to customize and start using efficiently. I wouldn't go with Emacs unless, or until, you have time to read and learn before actually needing to use it much.
I used Cream (Vim) briefly, but there was nothing special about it either way. I can't imagine going back to Notepad. I think I would love jEdit if I didn't dislike Java so much right now. It's really a great program.