I only discovered this website because I happened to check out a book written by someone who has contributed to the site, so in case you didn't know that Bess of Hardwick's letters were online, either:
http://www.bessofhardwick.org There's also a lot of supplementary material on her life, and on early modern language and letter-writing, so I plan to spend a lot of time with it once my end-of-year grading is done...