Fenixp: Well you can always provide detailed feedback, that's usually as important as programming itself. Participate in betas, post your findings on discussion boards, you know, that sort of thing.

edit: Or just try to get into non-programming bits, like creating assets.

Fenixp: edit: Or just try to get into non-programming bits, like creating assets.

Catshade: Translations from English to your native language is another thing to do.

Fenixp: edit: Or just try to get into non-programming bits, like creating assets.

Wishbone: One thing programmers are often no good at is creating assets. Every game needs graphics and sounds, every program needs stuff like icons.

Navagon: So many otherwise wonderful programs have atrocious UIs.

Psyringe: Beta testing, suggestions, translations, as has already been mentioned ... some projects also need people to do user support, public relations, documentation, presentation, forum moderation, etc.

Also, if you can already do code injections for other games, you could try a hand at programming small additions. Since you're talking about open source projects, you can join one, install the respective IDE, look into the code, and experiment with it. I migrated from a beta tester to a code contributor (without ever having been schooled in the programming language) in one project.

But it's hard to answer this question on such a general level. Why not pick a project that you really, really like, and ask its developers what you could do for the project?