This. Notepad++ has been my goto for years. It's tabbed, it does some highlighting. Opens literally anything. I've never wanted for more than Notepad++ offers by default. And if I did... there's plugins.

I know a bunch of people who swear by UltraEdit too. I think Notepad++ vs. UltraEdit is like the far tamer Windows version of Vim vs. Emacs.

I swear by Autosave. My favorite IDE is N++ and a Powershell window. I code in N++, then click on Powershell and reload the already-saved file.

And a compare plugin does exist as well, it's functional.