Over the years of using Joomla! I've always wanted and tried to give back in some way. There are so many ways of giving back to the community and I have to say I think I've tried them all now. From meetups, donations, coding, writing extensions and plugins all the way to just talking about and sharing my passion for the CMS.
Joomla User Groups and Meetups
Almost 4 years ago I started the first Adelaide Joomla User Group meetings after attending my first Joomla!Day here in Sydney. Going back home to Adelaide all inspired I quickly jumped on the Joomla.org.au forums and announced the new group. Immediately there was a lot of interest and the group grew over time and is now run by the guys at AllTraders. Good work guys, keep it up.
Online Forum Support
Forums support was another way I tried contributing back to the community. It is great in a way that you can help someone across the other side of the world troubleshoot their Joomla problems or give advice to others but sometimes it is a little hard to understand what is really going on with a website without having a good look inside at how and what is being used. I still do contribute on forums but not as much these days.
One of the benefits of contributing on a forum is that you also develop a public profile of your expertise and knowledge.
Bug Squashing and Code Contributions
Other ways I've tried contributing was in code and bug squashing and testing. I have to admit this didn't last very long. Personally as a business owner and primarily an implementer rather than an extension developer I found this to be a bit more time consuming than devoted developers would. A lot of the bugs that I did find in Joomla were usually already reported and tasks were already assigned to someone to fix.
Goes to show that the Joomla! Bug Squad are doing an amazing job squashing and securing each Joomla release.
Joomla! Magazine
This is one of the more challenging contributions to the Joomla community but very satisfying when you see the feedback and results from other readers. After taking several weeks to write one article and going through many revisions I finally get something worthy of publishing. Thanks to Brian Teeman, Anthony Olsen and Robert Vining for indirect and direct influences on how and what I write on blogs and the Joomla! Magazine.
If you'd like to see my contributions you can do so via my author profile on the magazine site.
Joomla!Day Volunteering
This doesn't come by very often but when it does I like to do what I can. Sometimes I bite off more than I can chew but standing back and getting assigned tasks that focus on personal strengths I think is the best approach.
Hence I'm Twittering a lot for the up and coming Joomla!Day Sydney, Nov 5-6th.
Presentations and Talking to Others About Joomla
I haven't done many but where I can and when I can I'll do presentations about Joomla and the specific things I love about the CMS. The last major presentation that I did was for OZeWAI on Joomla and accessibility. It turned into more of a why I love using Joomla to build accessible websites than a presentation on Joomla's accessibility. 
Joomla! Twitter Team
Last but not least and my favourite, the Joomla Twitter team! People actually get paid to tweet these days and it is something I seem to do quite a lot of on a daily basis. Whether it is sharing relevant Joomla articles, search engine optimisation news and techniques or general talk about what I'm having for breakfast and dinner, people seem to want to listen and comment on what I'm talking about. So contributing to the new feed that goes out via the official Joomla channels is a perfect and FUN way for me to contribute back to the Joomla! community.
How Can You Help Out and Contribute
Well, you can do any of the things that I mentioned above. Start a Joomla User Group meeting, contribute to bug squashing, help out on the forums, write an article for the Joomla! Magazine, join the Twitter/Facebook team or just get out there and spread your love for Joomla.
There are also a few other articles out at the moment that also talk about the same thing in regards to community contribution.
Stand up and take part. It is a fun and enjoyable experience meeting and learning from other people that love Joomla!