Alternatives for Notepad++
1. TextEdit: Mac OS X is shipped with TextEdit default editor just like we have Notepad for Windows, it is much better in features as compared to Notepad like support for regular expressions but does not have plugins and other features like syntax highlighting, String operations.
2. Sublime Text: Its one of the best Cross-Platform text editors that are available in the market. Works on All major Operating systems. As Notepad++, Sublime Text do have plugins support which makes it powerful choice for Mac OS X. Only thing is it has a Proprietary software licence.
3. BBEdit: This is yet another good alternative. Features include : Search and replace,syntax colouring for major programming languages, code folding, FTP and SFTP support, AppleScript, Mac OS X Unix scripting support, text and code completion HTML markup tools and pattern (regx) matching support.
4 jEdit : Its is a powerful text editor with hundreds features and plugins. Its a free software and its source code is released under GPL 2.0
Some features :
Works on Mac OS X, Unix and Windows Platforms.
Supports Syntax highlighting for over 200 programming languages.
Auto Indent feature and Word Wrap
Its highly configurable and customizable.
100s Plugins and Macros supported that can be downloaded using Plugin Manager.
5. Smultron 7 : Its is a Paid Text Editor that you can download from the App Store. It is very powerful easy to use editor wit many helpful tools.
If you haven't find the right one you are looking here are some more ...
10. SubEthaEdit 4
There are a lot of free and paid text editors available for Mac OS X. Though there is no Notepad++ for Mac OS X, you would surely find a substitute.