I find both calendars and tasks lists to be indispensable. My days are busy with much to do in all the principal fields of living, from work to family. I cannot remember and prioritize it all without written aids.
Once upon a time, it was all written, literally. I used pen and paper. That is the best way because it forces you to slow down, think about what you are planning, and consider your options. With productivity pressures rising, however, the time for it has grown increasingly hard to find, and so I have succumbed to the lure of the digital age.
Google Calendar with the addition of a utility called Remember the Milk was the one I chose. It had the required flexibility and was available wherever I could log onto the Net. Privacy concerns and the drive of service providers to force us all into a subscription-based fee model have driven me away from that, though, and now I use local software. Each morning, I review the day's docket (as I call it), edit it as needed, then print a copy with the hourly schedule on one side and the tasks list on the other. Returning to my favored pen and paper methods, I then change and note it as the day moves on to accommodate this unstable, ever changing world in which we live. At the end of the day the usually much written over docket becomes a primary source of my journal entries.
Were I to place less importance on the security of such personal information, I would use a remote service e.g. the aforementioned RTM and a handheld Net access device. More and more, however, data we keep in "the cloud" is mined by various parties for their own financial advantage and for more sinister purposes, and those monthly fees they all now want to charge us have become onerous. I consequently find myself falling back on a docket I control exclusively. I doubt I ever again will trust a service provider to keep good faith in that.