After a year of running this, it is amazing how many people really want to know how to map the Underdark (all three levels) and fit all the bits and pieces created over the years into one map.
My answer... you don't. While I started the campaign in the drow empire, I can tell you, the players haven't actually gone more than 300 miles from the place of slave origin. Amazing isn't it? Try crawling through little tunnels and see how far YOU get.
However, I found these particular map pieces (which fit together) most interestingly, as are the various rolls the creator established. He essentially made the Drow Empire
easier to do. I highly recommend it and agree with his reasoning. Underdark is TOO VAST to map in detail, but that's no reason you can't fill in little pieces of it. In fact, take all of the Wizard's stuff and just find a hex to plug em in. That easy.
I also have a liking for Gozzy's random generators
for their ability to do underground tunnel and cave combos for combat purposes. And you know it, they fit right into Maptools.