The US Federal government will match the amount a presidential candidate raises ($250 per individual). There is a slight caveat. You must receive at least 5% of the popular vote, which typically means the money goes to the two party system. That's not very fair, but what is fair is this... the source of the funds come from a voluntary tax you pay on your income tax form.

Sources:
http://en.wikipedia.org/wiki/Matching_funds#In_politics
http://en.wikipedia.org/wiki/Presidential_election_campaign_fund_checkoff