Although there are many ways to give back to "the community", most programmers don't. Usually because they don't realise there is a community, or because they just don't want to be part of it. Being part of "the community" takes time, and if you want to make most out of it, lots of time, even.

Everyone who is part of the community, also gives back. The thing that's given back most is time, to help people. This is good, because there's a great demand for help. CPAN modules are another thing, but I'm not sure if that's always a good for the community. Some who already donate time and/or code, also donate money to The Perl Foundation.

The money thing is a good option if you don't want to be part of the community, but do want to help out. I think that especially more companies should donate. If only just 0.5% of what they earn with Perl. But that's just my opinion.

But really, not giving back anything is also good. Perl is free software, and even if you hate sharing your code, experience, or money, you are still allowed to use Perl.

I structurally "give back" in the form of CPAN modules (most importantly DBIx::Simple), help (in EFnet #perlhelp mostly), and money. Occasionally, I write something that people find useful, like perlcheat and perlpodtut. The latter still needs to be submitted to p5p. :)