Gallica is the digital library of the Bibliothèque Nationale de France (BnF) and is one of the best freely accessible digital archives online, crammed full of brilliant historical sources. It’s fairly easy to navigate, and you can register to save documents and books to your digital workspace.
I’ve personally been using it a lot lately to access all the 19th-century editions of my medieval primary sources from the comfort of my bed, instead of having to trot all the way out to the Bodleian Upper Reading Room!
Word Tools: Thanks to the wonders of the internet, there are now various Latin word tools that will tell you not only what any Latin word means, but also that it happens to be a genitive singular future passive participle, or whatever the ‘case’ may be.
Whitaker’s Words – My personal favourite, partly because it does take into account some medieval spelling and vocabulary changes)
Medieval bestiaries are essentially animal encyclopedias, ranging in subjects from the domestic cat, to the exotic elephant, to the fantastic phoenix or griffin. They were more theological than scientific in nature, focusing on the moral or allegorical dimensions of the natural world. Loads of fun to be had on these sites clicking through the indexes of animals or admiring the beautifully illuminated illustrations.
Two levels of Latin tutorials (not as helpful for the grammar, but really good for medieval Latin vocabulary from common types of medieval documents), some paleography tutorials, and a couple other goodies.
(Mis)Adventures of a Medieval History Student at Oxford