Day One is a simple, beautiful & powerful journal app that syncs across all your iDevices using iCloud or Dropbox. Writing on a consistent basis is majorly beneficial to making sure you stay at the top of your creative game. Also, my main resolution this year was to share less and keep more. This was fueled by things like the time and energy I spent on social networks, my motives for sharing the things I did, and how both of those things affected the important things in life. These things were already going through my head when I read this post by John Saddington. So everything I would normally share goes to Day One first.
I also keep sermon notes, quiet time journals, quotes from books, thoughts for blog posts, etc. It also has a lot of geeky features like being able to write in markdown and such.
The kicker for me is that it's JUST a journal app. You can keep these same things in Evernote, and it's definitely a beautiful app; however, I use Evernote as a place to store design inspiration. For me personally, it would be distracting to keep those things in the same place.
The iPhone/iPad app is $4.99, the Mac app is $9.99 and are both completely worth it. You can also check out how other people use Day One.