In 2003, a Bush-administration official claimed that Pagans don't do charity work. I have heard this claim in other quarters as well.
However, there is a lot of service to the community and charity work being done by Pagans; it's just that we don't always get recognition, or seek it. There's a fascinating discussion of why there aren't many specifically Pagan charities at the Wild Hunt (see the comments section) and an older Witchvox article from 2003 musing over the very same topic.
Just last week, Jarred at The Musings of a Confused Man highlighted a charity that he is involved with called Kiva, where people can give microloans directly to people in the developing world.
I know personally two Wiccans who go to a homeless shelter to help out on Christmas day. (I bet they don't wear pentagram T-shirts there.) There must be many more.
Pagan chaplaincy for hospitals, the military, prisons and universities is another very important service offered by Pagans, in both the UK and the US, and all the chaplains are volunteers. It can be difficult for chaplains to get recognition, especially in universities.
Lots of covens, groves and hearths hold fundraising drives. Sometimes the charity they give the money to declines it, or doesn't acknowledge to other donors that it is from Pagans.
To me, Christian charities always seem like a thinly-veiled attempt to evangelise. You know, "look how nice Christians are, helping the poor and oppressed; that's why you should become a Christian".
That's why Pagans support (and get involved in) secular charity work: because we're not interested in making converts. And that's why Pagan charities are usually focussed on specifically Pagan issues, because other charities don't address those issues.
In fact, there aren't that many charities specific to other religions either, though many religions have an ethic of service. For instance, Sikhs give 10% (yes, 10%) of their income to charity, but there are no specifically Sikh charities that I know of. Jews are very charitable (Jewish housewives have a row of jam-jars labelled for different charities on their windowsills and put spare change in them, apparently) but I can't think of any internationally-known charity that is specifically Jewish. And so on and so forth for all the other major religions, but no-one accuses them of being away with the fairies and not caring about others. I expect Pagans donate more to environmental causes and animals, but that's good because other people always seem to be raising money for cancer and kids, but never for wildlife or oppressed tribal peoples.