There is an amazing volunteer effort to produce and air radio ads for Dean in Virginia, Tennessee, and Wisconsin. Donate to the cause and spread the word to everyone you know! Because the ads are totally produced by volunteers, these donations do not fall under the same restrictions as donations to an official political campaign -- non-citizens can donate, and there is no $2000 limit.
Even if you think Dean isn't going to win, remember this; the more support Dean has, the better the Democratic position will be in November. Dean leads; the rest follow. He has already done tremendous things for the Democratic party. Your support for him will continue to have a positive effect even if he doesn't win the nomination.