iOS: LifeTopix is actually one app, available for iPhone, iPod touch and iPad, with 12 interconnected "sub-apps" that all share information. Instead of entering an appointment into iCal and then having to add it again to Tasks or another mobile to-do manager, LifeTopix lets you enter your information once, and it shares your appointment and any relevant information across all of its modules.
LifeTopix allows you to enter items like your travel plans once in your calendar under "Events", and then access those same travel plans in "Shopping", where you can add a list of things you want to buy in advance of the trip. You can then head over to "Travel and Places" to see all the information you need to review about your trip, including your itinerary. This way you don't have to re-enter the same information into four or five different applications and services to keep track of them all.
LifeTopix is $2.99 in the iTunes App Store, and requires iOS 4.2 or later to run.