To Do list software is very subjective to how you work and what fits into your style…
I have tried many todo list apps including: Voo2do, Todoist, Toodledo, and even DontForgetTheMilk…..
VitaList is still my favorite. I had temporarily abandoned it to try some others, but I keep coming back.
It integrates with my Google Calendar (iCal); it sends me email and SMS reminders; I can group actions by project and context; it has a mobile web version; and it is color-coded 
Vitalist is perfect for anyone needing to get things done. Easily organize your actions and projects online. From grocery lists to business projects, track it all with Vitalist.
New iPhone Version at iPhone.Vitalist.com
PS - Nozbe looks real good too…but would not be free for how I would use it. I may give it a whirl though to see if it is better suited for my purposes.
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