The Texas Death Certificates on the Family Search pilot site (http://pilot.familysearch.org/recordsearch/start.html#start) have been a great help to me. I have been able to prove many parent-child relationships with them. The most exciting find was being able to prove my 3rd great grandmother's maiden name which was given on the death certificate of one of her daughters.
Not free, but low-cost. Mid-Continent Public Library in Independence, Missouri offers an out-of-district library card for $20 (annual fee) to access many genealogy databases from your home computer. It's a great resource for the cost as single subscriptions would be well over $100. Check it out at http://www.mcpl.lib.mo.us.