Well, I'm sure there are others that can chime in with other examples, but I can start.

Let's start with the beginning. McCormick makes the argument in Origins of the European Economy that the crucial moment in the development of the medieval economy came with the Abbasid Caliphate came to power and the initial conquests ground to a halt. This meant that the supply of slaves provided by constant conquest had finally dried up. This theory is partially supported by Michael Brett who made the argument that the trans-Saharan trade routes sprung up not because of the demand for gold, but because the Bilad al-Sudan was a great supplier of slaves at around the same time. This increase in the demand for slaves coincided with the Carolingian conquests of the pagan regions in what is now Saxony. The European supply of slaves continued throughout the Middle Ages to a certain extent. For example, the Genoese colony at Caffa regularly supplied the men who would become Mamluks. The Genoese colony at Caffa and others on the the Black Sea such as Killia also supplied timber, grain and other bulk products.

Even before the exportation of slaves, Venice did a tidy trade in salt. This was a lucrative product for the Venetians and the city exported the product well into the modern period when the Serenissima was finally conquered by Napoleon.

Additionally, as the Genoese and Venetians began to take over the Aegean islands, their colonies began to export Alum.

Europe also supplied the Muslim world with wine. Islamic law bans the consumption of alcohol, but that didn't stop people from buying it.

The Narbonnaise (the region around Narbonne in southern France) was the main producer of honey throughout the Mediterranean and oversaw a lively trade in the product until sugar began to become more widespread in the thirteenth and especially the fourteenth and fifteenth centuries. This process destroyed the economy of the Narbonnaise. For more information, see Larguier, Le drap et le grain en Languedoc: Narbonne et Narbonnais, 1300-1789 and Le Sucre by Orfelley. Sorry they're in French, but they're the best source for this stuff.

Europe also exchanged silver for gold in north Africa. The northern shores of the Mediterranean developed a gold standard for currency because the lack of gold in Europe (the gold mines of Poland and eastern Europe would not be opened until the early modern period) meant that the demand for gold was high and made it a valuable currency, whereas silver was more abundant. Silver was also the product that China wanted the most throughout the medieval and early modern periods. The British importation of Opium into China during a much later period was a reaction to the fact that they wanted to stop spending all their silver in China, but I'm sure I'm oversimplifying matters and perhaps a sinologist or an modernist can flesh this out. That said, China wanted silver and lots of it. For information on European currency during the Middle Ages, there's a really nice book published by Cambridge some time ago. I can drag out the citation if someone's interested. For the China bits, this should be corroborated my any number of sources. For a fun book, check out Vermeer's Hat. It's about the early modern period, but still applicable.

The biggest money spinner for Europe, however, was finished textiles. The highly urbanized Low Countries specialized in finished wool goods. Florence too also exported woven and died wool. There had been a demand for wool outside of Europe for hundreds of years by this point (see The Silk Road in World History). One need only look at the doors of the Florentine Baptistry, paid for by the cloth finishers guild, to understand the tremendous wealth to be had in medieval European textiles.

I'm sure I'm missing out on other products, notably arms and armor, but I'll let other take those on.

Can you please be a little bit more specific about when during the Middle Ages?