Juice is a quick and easy energy tracker app that shows the correlation between sleep, nutrition, exercise and energy levels.
iPhone and iPad apps tagged "daily journal."
Feel-Better is a Multi-Media Diary for Recording Thoughts and Feelings
Without being an expert on positive psychology or the benefits of journaling, it’s difficult to speak to the benefits of recording emotions and thoughts in a journal or diary. Benefit or no, if you’re interested in keeping a journal then doing so on your mobile device seems the most practical way.