I'm not 100% sure if Derek plans to host some sort of D&D Next (5th edition, not yet released) Arena event (which would be pretty easy, actually) or if he meant the Pathfinder Arena.
Dungeons and Dragons doesn't really sell miniatures anymore, although they do have the
Dungeon Command sets.
Pathfinder, which is a revised version of the Dungeons & Dragons version 3.5 rule set, sells all sorts of awesome prepainted miniatures. A new set goes on sale later this week, actually. Their miniatures are easily used for either game.
The three sets of miniatures currently available are:
Rise of the RunelordsShattered StarSkull and Shackles - released later this week
The RPG market is considerably different now.
The major players are currently Pathfinder, Dungeons & Dragons, and the new Star Wars RPG called "Edge of the Empire."