These sites have proved useful to me in the past.

Adams and Stephens “Select Documents of English Constitutional History”

http://www.archive.org/details/documentsofengli00adamiala

Sadly, Don Aitkens handy indexed online version is no more, but could still be accessed via the wayback machine on 04/04/2011

http://home.freeuk.net/don-aitken/ast/astintro.html

Historical Charters & Constitutional Documents of the City of London

Walter de Gray Birch

http://www.archive.org/stream/historicalcharte00londuoft

Numerous Documents from Henry V's Chancery

http://etext.lib.virginia.edu/toc/modeng/public/AnoChan.html

Various Documents from English sources,

http://www.british-history.ac.uk/period.aspx

Records of the Scottish Parliament (Browse by reign)

http://www.rps.ac.uk/

Various items from Yales Avalon project, these the pre 18th C ones.

http://www.yale.edu/lawweb/avalon/pre18.htm

The Electronic Middle English Dictionary

http://quod.lib.umich.edu/m/med/

Las Siete Partidas of Alfonso X Il Sabio

-Spanish Law, The Seven Part Laws of King Alfonso X "The Wise",

http://faculty.washington.edu/petersen/alfonso/alfonsox.htm

Privy Purse Expenses of Elizabeth of York:

http://www.r3.org/bookcase/wardrobe/ward1.html

A collection of 15th C Grants of Arms, both Personal and Corporate.

http://verysleepy.itgo.com/grants.htm

Grant of arms 1469 for Peter Hellard, Prior of Bridlington

Sven Norén's translations of Swedish Awards of Arms and a Knights Oath

http://www.geocities.com/sven_noren/Patents/index-eng.html

An excellent article, covering much the same ground as I am.

http://www.sca.org.au/scribe/articles/period_text.htm

Baron Steffan ap Kennydd's translation of a 1230 Coronation Service for the Kings of France

http://www.eastkingdom.org/artsci/articles/ordo_of_reims.html 

A European Online Documentary Archive, the enormously promising,

http://www.monasterium.net/

Full transcriptions and photographs of huge numbers of extant documents from central europe.

The fifty earliest English wills in the court of probate, AD 1387-1439.

Copied and edited from the original registers in Somerset House by FJ Furnivall, 1882. EETS.

 http://www.archive.org/details/fiftyearliesten00probgoog