Sprite is a term that comes from the video game world, referring to a 2d graphic applied in screen space. (As opposed to applied to an object in a 3d world, which would be a "decal.")

The Dundjinni forums are, indeed, an excellent source of building-scale map objects like tables, treasure chests, and fireplaces. It's a little lean on town-scale objects like buildings, but I think it does still have some. If you can find it, there is a collection of objects gleaned from those forums called the CSUAC. I forget what that stands for, and it's sometimes difficult to find a source, but if you can locate it, it's well worth the significant amount of time it will take to download.

There are also some resources here in the Mapping Elements forum, although our collection is relatively small. We do have quite a few brushes for Photoshop and Gimp, though.