I used to use Remember the Milk. It integrated well with the Google Calendar. They have a free app now: https://play.google.com/store/apps/d...milk.MobileRTM
They have forums and a large group of users, so it might be worth vising the website and giving it a try.
For people using Jelly Bean, like on the Nexus 7, you might want to look at the "Now" feature as it does reminders based on calendar entries. I just got Jelly Bean pushed to my phone!