First off, you'll find out that any Mac program, compared to Notepad ++, is much more intuitive and easy-- you'll save lots of time.
With that said, I recommend
Coda. Why? Because if you start off with a FTP program and various text editors / subversion apps, you'll get fed up fast. Coda allows you to do most everything you'll need to (assuming you're a web designer OR will use FTP). Once you get used to a text editor, it's hard to switch because you get used to the colors. Although, sure, you can change the colors- it's annoying to do.
Expresso is also another great choice, and like Coda, it is an "all-in-one" sorta app.
If you simply want a text editor, try
Smultron (free)- it's fast, easy, and lightweight.
Textmate is also a very capable text editor. Try
CSSEdit for faster CSS editing, if your a web designer.
Hope this helped out.