For cultural information, the Viking Home Page has plenty of information for the far north, while the Gaelic Homepage has handy information for heading a bit further southwest.

Project Gutenberg is an excellent resource for classical literature. An excerpted Malleus Maleficarum is now available on the Web. The Encyclopedia Mythica has a lot of nice summaries. The Aberdeen Bestiary is a delightful authentic reference with images of the original illuminated manuscript along with the Latin and translations.

If you decide you'd like to dress the part for your character, take a gander at Gaukler Medieval Wares.