Mac users have many choices when it comes to note-taking apps, and MacNote3 is a solid choice for anyone wanting one with good search capabilities and AppleScript integration (especially if you're a fan of the venerable built-in Notepad app of yore).
MacNote3 is a heavy-duty version of the original MacNote, with a good balance between simplicity and power. In addition to basic formatting and editing controls, MacNote3 lets you use links that can launch anything from URLs and files to messages in Mail, which makes this app perfect for to-do lists. You can also search for strings across multiple notes, and you can incorporate AppleScripts, too. The developers have some good suggestions for this, including the ability to automatically generate e-mails from templates.
You can see MacNote3's old-school roots in its bare-bones interface, but not always in a good way--and it can take some time for novice users to plumb the depths of this app's capabilities. For anyone who has specific needs, though, especially around scripting or search, MacNote3 can be a good value. This shareware app comes with a 30-day trial.