Notae is a full-featured and lightweight notebook with instant full-text searching of notes and complete import and export functionality. It can even read your notes out to iTunes, and thus your iPod. It includes a Mac OS X Service to grab any text or file selection and keep it as a note. Its open document format (XML or SQLite) allows for other creative uses. Really, it's TextEdit on performance-enhancing code.
You can also drag in PDF or WebArchive files and Notae will keep those, too. In fact, you can import URLs and create Web notes to keep pages around as they were, not as they are. Drag in URL clippings or URLs on the clipboard and Notae will make a Web note.
Drag in a folder of text, PDF, Web Archive, HTML, Word, text, and/or text/URL clipping files and Notae will do the right thing with each one.
Notae both imports and exports to plain text, MS Word, Word ML, XHTML, RTF, and RTFD.