Periodically I look at the sorts of tools that you can use to remember that it's someone's birthday. Here's the current things that put birthday reminders in front of me every day.
The 10,000 lb. gorilla of birthdays is Facebook, which offers a nice simple interface to send a one-line birthday greeting. You could visit Facebook daily just for birthdays and not much more, and be reasonably satisfied with the results. The site offers several convenient ways to send gifts via Starbucks, iTunes, and Target.
The up and coming wannabe of birthdays is Google Plus, which puts birthday notifications on your Plus home screen. I'm not 100% certain where it gets its birthday information from – whether it pulls in details from you Google Contacts data, or if it's just self-reported birthdays on your Google profile.
LinkedIn has birthday alerts as well, but some people have complained that the reminders are annoying. There's no apparent way to turn this feature off in LinkedIn.
Finally, I have a new Contacts + app running on my Android phone, and it reaches into your contact database and reminds you about people who have birthdays today. The handy thing about it is that new birthdays show up as notifications with a one-click to a screen that offers you lots of ways to contact someone, so that if you were to want to send someone a postcard (a few days late, alas) you could be ready for that task.
I still don't have a great way to routinely get birthday postcards to people on time – that would take a level of daily or weekly commitment and organization that I'm not yet ready to take on!