http://taskwarrior.org/projects/show/taskwarrior
alias due='task rc.calendar.details:full cal'
to get a nice representation of tasks. you might wanna combine taskwarrior with remind.
http://www.roaringpenguin.com/products/remind
it allows you to "program" your calendar dates. A little caveat if you're on osx you may need to patch it otherwise it will have a 30 or 10 second startup delay