D&D Miniatures is a line of plastic, pre-painted miniatures from Wizards of the Coast. More than just a set of collectible playing pieces, you also get a streamlined version of the D&D combat rules for skirmish battles. Similar to Chainmail, for those of you who remember their earlier offering, but closer to the D&D rules.
Supporting the D&D Miniatures is the Miniatures Handbook. With info for both D&D as well as the miniatures rules, it is a very useful resource. My favorite part: rules for solitaire play in a randomly generated dungeon.
The solitaire play rules can be expanded to cover pre-made, semi-random dungeons (like the sample dungeon on the Wizard's website). Inspired by this example, I have created a sample dungeon of my own and am working on more.