Fat Dragon Games, those makers of awesome, high-quality paper scenery, are having a weekend sale to commemorate the 4th of July! To this end, their entire line is 25% off! You'll want to hurry, though--the sale ends Monday, July 5th. Whether you want 2-D or 3-D scenery, inside or outside the dungeon, Fat Dragon probably has something that will work for you.
I can especially recommend their E-Z Dungeons, Copper Dragon, and Dragon Tiles lines. If you're a budget gamer, the Copper Dragon line of 2-D scenery is an especially good deal. If you're looking for something a bit fancier, you could try the E-Z Dungeons Deluxe product.