The un-insurable children and adults with pre-existing illnesses can now obtain some insurance via this new Affordable Care Act provision, passed in Spring 2010. This is the PCIP plan. Many other provisions will role out until 2014 when Health Insurance Exchanges will be up and running. An excellent timeline is here.
Children can stay on their parents health care plan until age 26. Small businesses can obtain tax credits.
Some PCIP plans are administered by the Federal government. In other states including California, the state administers the pre-existing illness plan. See this link. CA plan.