whiteboard with a list, you can also get magnets that have bulldog clips, so either get a magnetic whiteboard or stick them on the fridge.

I've also used a corkboard with pins, but with your little ones Pandora I'd probably skip that.

One of my girlfriends, with a blended family of 4, uses excel to keep track of access visits, appts etc, she also has this in outlook and synched to her phone. Another uses the calender section of gmail.