Send some merchants up to the Russian lands (Smolensk, Kiev, sorry cant remember all of the province names). There are some quite profitable gold resources up there.

Also at the bottom of the map in the Dongola province (below Alexandria and Cairo) there are some good Ivory and Slave resources that are worth good coin.

Finally one other and probably the most sort after by the AI is the silk around Constantinople and Nicaea.

Make sure you take a pack of merchants with some assassins, these resources there are usually highy pursued by the AI. But as whiskyghost mentioned it can be all relative to where you are located on the map.