Am currently reading
Medieval Underpants and Other Blunders: A Writer's (& Editor's) Guide to Keeping Historical Fiction Free of Common Anachronisms, Errors, & Myths and other Blunders by Susanne Alleyn.
I thought it was worth the low Kindle price for the section on underwear alone.
However, there's an entire chapter on peerage, titles, and how to address the nobility, and it's made me realise I've completely cocked up in this area!
(I've been using surnames for lords, thinking I needed them - which is a massive boo-boo if keeping to the fineries of English peerage).
Anyway, a potentially interesting read in the first place:
http://www.amazon.co.uk/dp/1490424032/?tag=brite-21
However, for free online sources dealing with how to name members of the nobility in fiction or fact, how they are titled and addressed, here are a couple of potentially useful links:
Addressing People with Titles | Forms of Address - Titles and Titled People
British Titles of Nobility
An additional point - according to Alleyn, no English king was ever addressed as "Your majesty" until Henry VIII and after.
Food for thought!