A link to the next county over from me, maybe good for a ballpark idea.
http://inetdocs.loudoun.gov/b&d/docs/permitguideline_/deckdetail-1/deckdetail.pdf Locally available materials can be different as well as local regs.
Also a limited span calculator, but from an authoritative source;
http://www.woodworks-software.com/us/downloads/spancalc.php Use with care.
A good direct article on sizing by Ed Levin is in the first volume of the guild design workbook.
http://store.yahoo.com/tfguild/deswor.html
