TextEdit is the best and comes bundled with OSX. If you want to make it without any text formatting, go to menu “Format > Make Plain Text” (or shortcut 'Command+Shift+T”. You can also set this non-formatting as default everytime you launch this app.
Click to expand.I would agree that TextEdit with Rich Text Format disabled is a good analog to the Windows Notepad. At the same time, TextWrangler that myflynn recommended is a good tool. It much more powerful and more like the freeware NotePad++ that is available for Windows, but it might not be simple enough for some applications. I have NotePad, WordPad, and NotePad++ withing easy reach on my Windows machines and both TextEdit and TextWrangler on my Mac's Dock. I find I use TextEdit much more than TextWrangler. It's a case of which took best fits the job at hand.
Extra features can sometimes get in the way. Gcc compiler for mac.