Further to my most recent post about Medieval armour, there's an interesting blog called How To Make Armour. This provides some insights into how various types of objects from the period can be made, which could come in quite handy when trying to draw such things. I've always found that it's much easier to draw something if you know how it's constructed - that includes the human body, armour, cars, etc.
Similar information can also be found at Age of Armour, which also includes a some great photos of compeleted commissions.
Medievalists.net may also slake your thirst for further knowledge about the Medieval world.