Meemo: a good and free app for taking notes in categories and with a diary function. All notes are stamped by a date and time. Special feature is the backup function: the SQLite database can be converted to a CSV file using the Mac tool “SQL-” and thus be edited and analysed in more detail afterwards.

It is also a good tool to get some ideas sorted.

http://itunes.apple.com/de/app/meemo-note-diary-alarm/id386598059?mt=8