4th Edition's scale of 5 feet to a square can lead to cramped, tiny encounters if you directly convert maps from older editions. Before you run an adventure, sketch out each dungeon or encounter area on graph paper and see how much room is available for maneuvering. Ideally, even when the party and their foes are locked in melee there is still space for creatures to move around the battlefield and threaten either side's back rank.He also takes a look specifically at the minotaur caves from B2 - Keep on the Borderlands and the entire steading of the hill giant chief from G1. (Be sure to swing by to snag the nice map of the upper floor of the steading, if for nothing else.) You'll need to log in to read this article, but Dragon is still, for now, free to the public.
Large and Huge creatures present trouble, since they usually took up less space as miniatures in older editions of the game. If you have the time, draw encounter areas on your battlemat or set up Dungeon Tiles. Place the miniatures for the encounter on the area, along with minis for the characters, and see how crowded the area is. Big creatures need a lot of room to maneuver. Try to avoid situations where a single fighter or paladin can either lock down all of the monsters or set it up so that only one Large or Huge creature can make melee attacks against him.
UPDATE: And now the article is gone?!? Not sure what's up with that. Er, if it comes back, I'll let y'all know. :/