You can see a good selection of medieval English recipes here. Ginger seems to be the most used spice. Pepper was perhaps the most prized; cinnamon, cloves and galangal also feature regularly (the last being a spice that is generally only seen these days in South-East Asian recipes). Other spices show up more rarely. Medieval cooks seem to have made do with whatever spices they could get their hands on. Sugar was also used in "spice" blends like poudre douce (primarily ginger and sugar - recommended for fruit pies).

These recipes will have been for the wealthy though; less well off households would obviously be less able to afford spices. Does this mean medieval cookery would be bland? Not necessarily. There's a great variety of flavour in fruits, vegetables, meats and herbs. We're used to adding pepper to just about every savoury dish, and we'd probably miss it if we didn't, but it's not essential (salt, on the other hand, is more fundamental). Where spices offer some advantages (this is me speaking as a cook more than a historian):

• increasing the range of flavours
• strength of flavour (particularly useful with some of the period's cooking methods)
• keeping well, ideal for adding some flavour when there's not much in season
• going well with sweet foods (there aren't many herbs you'd put with cooked fruit)