CryptoTE - CryptoTE is a text editor with integrated strong cryptography.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
Notebook PEA - Protects your private notes with a password.
Daybreak - An intelligent to-do app that learns when to remind you
Paranoia Text Encryption - Paranoia Text Encryption encrypts text according to a choice of strong algorithms.
SilentNotes - A note taking app which respects your privacy.