This year I have supported three Open Source initiatives that I have probably used the most. Elgg, NeoOffice and Wikipedia have contributed greatly to my ability to earn a living, learn a lot more than what I would have otherwise ever known and build and express a lot of ideas and concepts. These are not major contributions and they have been made in a personal capacity, but I do intend to push it up a notch every year and once the company steadies itself I will institute a proper program that will identify more initiatives and contribute a lot more.
A lot of what we are able to do on the web these days is possible due to the work of a handful of people who have often worked for nothing in return. If some of the software that enables us were to be billed at the level that most shrink wrapped software is billed, the internet as we know it would not exist today. You can argue about the validity and feasibility of that model, but you can't argue that all of us have benefitted greatly from it. Even though most of the stalwarts who have put together these things have not demanded money as a must-have in return for what they have created, it is a good gesture to make any contribution that you can make.
If it is possible for you, do try to find one of those that you like and contribute in whatever capacity you can.