Apple - Alternative for Notepad++?

It's not clear from your question what exactly you're missing -- I use Notepad++ on the PC and find both TextMate and TextWrangler to be reasonable replacements -- but you'll likely appreciate either TextWrangler's big brother BBEdit 9 or, if you can put up with its alpha nature, Sublime Text 2.

Sublime Text 2 seems to be the real powerhouse for people that are not satisfied with the heavy guns of Mac editors:

• BBEdit is now on version 10 and "still doesn't suck" (you mentioned it's free mini incarnation - TextWrangler)
• TextMate (either the venerable v.1 or the long unfinished but now open sourced v.2)

Marco Arment did a nice job of rounding up not only the why but some other editors to consider with Chocolat leading the pack behind ST/BB.

I've recently started using Atom - it's modern, lightweight, and does a metric buttload of different things.