It's easier if you just remind people about your birthday instead of expecting them to remember.  People aren't really thinking about other people most of the time and that's okay, they're not allowed for it!  

If you expect everyone else to remember your important occasions then you might have a tough life ahead of you because it's not a fair expectation.  Just come out and say "Oh hey it's my birthday tomorrow, buy me a cake/dildo/car/kangaroo/bet!" And I bet you any money they'll appreciate it more than feeling like an ass for forgetting.