I'm a sucker for a gorgeous, antique map. My friend Sarah and her husband collect historical maps from places they've visited, an idea I've been meaning to co-opt as maps really do make the perfect souvenir/conversation piece, and they look fantastic grouped together on a wall.
One of the best resources for antiquarian maps I've found is The Old Print Shop in New York. Founded in 1898, the shop's been at its current Lexington Avenue location since 1925 and was purchased in 1928 by Harry Shaw Newman, who was best known for bringing the work of 19th-Century lithograph makers Currier & Ives to fame (fun fact: he was apparently known as "Mr. Americana"). The shop is still family-owned, and is currently run by Newman's son and grandsons.
In addition to maps, they also have a wealth of modern and antique prints, photography, and art books, most of which you can shop at their online store. Here are a few of my favorites: