Contributing to WordPress Core
There are many ways to contribute to WordPress such as adding to the Codex documentation, participating in the support forums, testing, bug reports and so on.. But for programmers, such as myself, there is nothing more satisfying than being able to contribute to the WordPress core code. The way the WordPress development process is structured allows for anyone with decent PHP programming skills to have a go at tackling some WordPress coding. Just download the latest beta and start coding!
Submit any altered files as patches and then wait to see if they are accepted. There are always open tickets to explore that need bug fixes and testing etc. The WordPress Trac is a live and very active community of dedicated WordPress developers. So if you are interested in this aspect of WordPress then so you might want to head over and check it out.