According to numerous websites, there's a fair amount of D&D Miniatures information coming out of GenCon. Here's what I've been able to round up:

• GR has Q&A notes that tell of Underdark, the next expansion due this November, containing a Deep Dragon figure, Elminster, and "a Drow", as well as an "arcane siege engine, war troll," and the words "aspect of ..." trailing off to nothing. There's also mention of "more huge creatures" in 2006, including some for Star Wars Miniatures, and a focus on Dragons in upcoming sets.
  
• Merric's D&D minis page has the regular and Epic stats for the Elminster figure, which is being given out as one of two promo figures at the show (the other being the Dark Naga). On top of various nasty spells of his own, Elminster has Mastery of Spellcasting, which lets him cast every spell each creature in his warband has once.
  
• Also at Merric's, details on the War Drums starter expansion coming in March 2006. The set promises updated rules, full-color fold-out maps instead of tiles, and adjustments "to accomodate any size figure, from tiny to huge and even beyond." Can you say Gargantuan or Colossal? I sure can. I hope they don't get doled out slowly at conventions, like WizKids' Galactus, though.
  
• This thread at Hordelings mentions several figures as confirmed. For the Underdark set: Xorn, a "X’endrick Champion (another Scorpion Clan Drow)", Half-Fiend Ogre, Dark Creeper, Grey Render, and Drow Arachnomancer. For War Drums: Wood Elf Ranger, Orc Mauler, Warpriest of Moradin, and Arcane Ballista.

More information will surely come to light in the days after GenCon, once attendees have time to digest what their innocent eyes bore witness to.