It's time to hog some diamonds! Spawn in the typical plains area with a lot of diamond ore in the ground.
The first batch of diamonds is located at -98 64 252. You only need to dig some 40 blocks into the ground, but be careful -- there is a pool of lava close by.
Another one can be found at -133 13 240 near the creeper spawner, and you will even see some gold ore nearby as well. The final spot with diamond and redstone ores is hidden at -166 15 257.