In early alpha I remember Minecraft videos showing slimes deep underground. I think you would attack them then they split into several smaller slimes. But I’ve never found a slime for myself. In what conditions can you find slimes? Are they definitely still in Minecraft?
Edit: As of Minecraft 1.5 or so, Slime spawning has changed yet again. Right now, Slimes will only spawn in certain chunks of your map, depending on the map’s seed. There are tools online such as this one that let you input your seed, and it will output the chunks of your map that will spawn Slimes.
Slimes spawn within 16 blocks of bedrock, in any light conditions. I think they were removed in the 1.2 Beta, but it is confirmed that they have returned in 1.2_01. Slimes spawned fairly frequently back in Alpha, but I believe Notch reduced the spawn rates by quite a bit since then. The 1.3 update increased the slime’s spawn rate yet again.