Ore Seeds mod allows you to conveniently plant seeds that eventually grows in to the four main types of ore in Minecraft which is Iron, Gold, Diamond and Emerald, which can be then conveniently farmed once set up. Each seed is crafted using nether stars and 8 blocks of the corresponding ore. This may sound expensive at first, but it becomes worth in the long run because it will continually produce the ores for harvest when taken care of.
Iron, Gold and Emeralds should be grown on using the Netherrack, another new item included in this mod, should be surrounded by lava, and must be grown in The Nether. Be careful of burning yourself and other items placed around lava though!
The Diamonds are grown on coal blocks surrounding lava but can be grown outside The Nether.