I've been using Notepad++ for a while now, but I noticed it doesn't have code snippets (I found the QuickText plug-in, but it doesn't work anymore), so I'd like to switch editor and my requirements would be:
What are you using?
The E Text Editor (clone of TextMate for Windows) is worth a look. It supports all TextMate snippets, has a file tree view (watch the screencast), has multiple themes, and starts up relatively fast.
Well, there is always Emacs. It does everything that you ask for, and a lot more. The only real downside is the learning curve (C-x C-s to save, C-x C-c to exit etc), but it's a myth that learning Emacs is hard. And you don't even have to learn that much in order to use it (like with VIM), learn the basics and learn more when needed.
Also, ErgoEmacs seems to be a good place to start. I wish I could have discovered it before getting too familiar with vanilla-Emacs. Oh well.