through 500 tons of goods over your ship. 

change the look of a house 1000 times.

click on a house 1000 times.

cultivate 10,000 tons of spices.

refill the norias with 10,000 gallons of water (no set # of times).

replenish depleated resources (ie. ore mine/stone quarry) 1000 times.

build 20 fishing huts on 1 island.

build 20 small storehouses on 1 island.

travel over 5000 nautical miles in your flagship in one game (ie. use it to transport 
items a lot, or simply move it a lot).

trade of 500,000 gold coins worth of goods with Al-Zahier or Richard Northboourgh 
(sorry for poor spelling of names).

buy goods from either Halarius (monetary) or Kareem (caravanseria) over 100+ times 
(can't remember the exact amount, sorry).

destroy your Cathedral after its completed. (hint... I know, its painful to think of, 
but simply save the game before doing the demolition an receive your gem reward and then 
load the game anew... you will still have activated the cheat and have won those precious gems!)

play the game for over 24 hours.....

start a game between 1 and 5 in the morning. 

play on Christmas day
(venice addon only- switch the special items on offer by the neutral parties over 100 times) 

All I can remember at the moment... will submit more in the future.