NOW LIVE! Into the Woods--new character species, eerie monsters, and haunting villains to populate the woodlands of your D&D games.

GM 'Tools'

If you're asking for actual things I use when DMing, here's a good list:

Homemade DM screen (made out of 2 manilla folders)
[ame="http://www.amazon.com/Chessex-Dice-Pound-Dice-Approximately/dp/B000X75BFE"]Chessex Pound-O-Dice[/ame]
[ame="http://www.amazon.com/Chessex-Role-Playing-Play-Mat/dp/B0015IUAAG/ref=sr_1_2?s=toys-and-games&ie=UTF8&qid=1328637627&sr=1-2"]Chessex Megamat[/ame] (with markers of course)
frankthedm's monster tokens glued to [ame="http://www.amazon.com/Gold-Crown-Bottle-Caps-gross/dp/B00023B72U/ref=sr_1_2?ie=UTF8&qid=1328637817&sr=8-2"]bottlecaps[/ame]. Flip them when bloodied (or any status really).
donjon.bin.sh for initiative tracker and random generators.
And most importantly, scratch paper and a pen.