For day to day task lists, in addition to my whiteboard for day-to-day use, I really like MS OneNote, but the lack of utilisation/sync’ing for smartphone/tablet/android means I need to look for alternatives.
As such I am currently trialling Google Tasks: There is an Android appcalled ‘GTasks’ which is so far simple but sufficient. It seems odd that there is no decent PC desktop app available (that I have found so far). However an app may not be necessary as I recently found the following better URL for better in-browser access to Google Tasks: https://mail.google.com/tasks/canvas
[update 2011-06-13] I’ve just tested using the GTasks Android app offline, and it worked well, allowing me to add new items, and auto sync’ing once I turned the Tablet’s wifi back on. (am now proceeding to buy the paid for version of GTask)
[update] There are also some Android apps (MobileNoter SE) that support the McrosoftS OneNote files directly (.one) which in conjunction could be a v handy option that I may experiment with for broader note taking.