DM Resources

World Building Resources

• The Cartographer's Guild is a great source for inspiration, whether you're plotting a map of your world or just trying to brainstorm sone interesting scenery.
• WotC Dungeon Adventures Index is great for finding just the right encounter or adventure to steal for your campaign's next session.

Computer Tools

• inCombat is a great status/initiative manager that will track pretty much any trait or condition you'd want in 4e -- it will even remind you to make saving throws and apply ongoing damage. It has a robust encounter export system, as well as the ability to search and import straight from DDI. Best of all, it runs in Adobe AIR, so you can use it on pretty much any platform! Highly recommended.
• iPlay4e is my go-to tool for managing either a single character on an entire party. Its integration with the fabulous inCombat makes it all the more appealing.
• Orokos is an alternative character manager for those who want a more traditional style character sheet. I personally prefer the layout and integration of iPlay4e, but Orokos is really nice nonetheless (especially if you want to just show a build to a friend).
• Donjon Random (everything) Generator - perfect for when your party really, really wants to know the name of that redshirt city guard.
• AnyDice is fantastic for making sure the odds on your clever new trap are just the right amount of unfair.

Table Toys

• Reaper Miniatures  are the classic for when you want to throw some monsters on the table. There's even a convenient figure finder for when you're looking for a very specific flavor of menace.
• Red Box Games makes some absolutely fabulous looking miniatures. They are classic fantasy with a truly distinctive look and feel.
• BattleGraph Dry-Erase Tiles are my default surface for drawing out dungeons. I love them because I don't have to worry about lining things up so that everything fits on a single grid mat, and I can feel free to expand in any direction and naturally if the situation or improvisation requires. Plus, it really cuts down on the meta-gaming players do when they see me place a room next to the edge of the drawing surface... Highly recommended.
• Litko Game Accessories are a great source for various odd and ends when you want simple markers to spruce up your table experience. I have gotten a lot of good use out of the Boundary Tokens for tracking zone effects, as well as the Raging Fire Markers and Torch Bearer Markers for tracking lights and various other hazards.