To-do lists are important to me. I am unable to remember anything unless it is in my calendar and/or on my to-do list. So finding at good To-do list has been difficult. The most important obsticle I have come up against is the ability for the To-do list application to be cross platform.
I have an iPhone, use a Macbook for personal computing and Windows at work, and I want it on all 3 platforms. I have tried so many applications that I can not remember them all, and most are only Mac or Windows.
The best of the best so far have been Omnifocus (Macbook & iPHone), Things (Macbook & iPhone) and Remember the Milk - RTM (web-based and iPhone). Although RTM works on all platforms, once you have used Omnifocus or Things, it just does not measure up with the user experience that works best for me. My solution seems to use RTM for office purposes (Windows primarily) and Things or Omnifocus for personal purposes. Not the best solution, but it does give me access to the work lists anywhere with RTM, and personal is always with me on my laptop or phone. It is the only solution close to good that I have been able to come up with.
Let me know if you are in the same boat and your solution!