I shared with you last week how I use Evernote for keeping track of my potential and future photo shoot locations. I also told you that I have a good but a very short memory so I need a really good way to keep and organise my to-do list. An app called 'Priorities' (from Hand Carved Code) helps me a lot in getting my head around all the tasks and things I have to do for my photography projects, my website, maintaining gear, etc. What I really like about this app is that it's really simple (so you're not distracted with unnecessary bells and whistles) but at same time it has all the functionalities that I need. To name just a few: ability to prioritise tasks and having sub-tasks, setting deadlines and reminders, integration with iOS calendar, cloud sync across all the iOS devices and the online version. The latter one, I think, is my favourite one.
Unfortunately, Priorities is currently only available on iOS devices.