I know that farming is eventually to be implemented, and i'd like to see something where you can plant different types of crops.
Perhaps corn, tomatoes, potatoes, etc...
In order to grow the crops, you would first need to take a seed or get the original block somehow from something (perhaps certain mobs would have a chance of dropping them? or a small number of them could be generated throughout the map.)
Then, in order to grow the seeds the player would have to plant them on dirt tiles that are directly adjacent to water tiles. Also, there could be some crops that would grow without sunlight (mushrooms, etc) in addition to crops that would require sunlight. Crops that are grown in sunlight should give off food that gives slightly more health when consumed. This would be a fair trade off seeing as how these crops have the sunlight requirement to grow.
By requiring crops to be planted adjacent to water squares, it gives water some real purpose in the game and this could easily turn land that is near water into very desirable property. It would also require players to make their farms look somewhat farmlike by make irrigation a useful farming stratedgy.