As discussed elsewhere on this site, there are various methods for funding Open Access journals. Two of the most prevalent to have emerged thus far are the "author pays" model (which is actually something of a misnomer, since costs are usually borne by the research funding institution rather than the author) and the institutional membership model. You can help advance the causes of these two models:
If you receive grants for your research, check with your funding agency to see if they will cover the costs of OA publishing. Many, including the NIH, NSF, and the Wellcome Fund, do. Here is a partial list of funding agencies that explicitly allow direct use of their grants to cover article-processing charges. Others are sure to follow, and you can help by engaging in a dialogue with funding bodies.
In looking for an OA publisher, you may find one that waives publishing fees, or heavily discounts them, for researchers from institutions with memberships in the publishing organization or institutional subscriptions to the journal. One example of such a publisher is BioMed Central (read about the perks of our BMC membership) and examples of journals include PNAS and Nucleic Acids Research.
You may also want to read Peter Suber's advice to faculty: What you can do to promote open access .