So in my SP game, I've decided it is time to mix things up and move underground.  I've just begun construction on what I hope is eventually a Moria-esque Kingdom.  This inspiration struck me after I dug a 8X8 hole down to bed rock (one of my favourite ways to stock up on Cobblestone).  A few blocks above bedrock, I began digging into the wall of my hole and after reading a bit of LOTR dwarven lore, I got the inspiration to move my playtime down underground.  
After building a long hallway, I began crafting the room for my lava forge (lava is currently being looked for), where I could craft and smelt.  Whilst digging there, I found the largest Iron deposit I have ever seen.  I got (and no word of a lie) 26 blocks of iron from this one single deposit.  There was also some of that blue dye, some redstone and a vein of five diamonds.  I am so glad I began digging here 

  This will be a prosperous kingdom indeed.