Goodsprings:

On top of the back-left grave in Goodsprings Cemetery (near the water tower), at the base of the grave marker. The grave is the only one in the area with rubble on top; the snow globe can be found amongst it.

Hoover Dam:

In the Hoover Dam visitor center, sitting on the welcome desk.

Mormon Fort:

In the Old Mormon Fort. As soon as you enter the fort, turn right, go all the way to the corner, and enter the door to the tower. The snow globe is located upstairs on a shelf.

Mt. Charleston:

In Jacobstown Lodge. The snow globe is sitting on the reception desk.

Nellis AFB:

Nellis Air Force Base, Nellis Boomer Museum. The snow globe is located on the table to the right, immediately after entering the building.

Test Site:

In the cocktail lounge of the Lucky 38 Casino. The snow globe is on the counter "behind" the middle cash register with a green lamp next to it (you must first speak with Mr. House to gain access to this area).

The Strip:

In the Vault 21 Hotel, on the nightstand in Sarah's average-locked room in the northeast corner of Vault 21, next to the buyable room. You can pickpocket Sarah for the keys if necessary.

Sierra Madre Casino: (Dead Money Expansion)

Located near Dean's Secret Stash in the upper levels of Salida del Sol North. From the southern-most entrance to Salida del Sol South (inside a house in Salida del Sol North), proceed down the stairway and out to the street, then look behind you for the entrance hole in the wall above. This area can be reached by going up the stairs located around the corner to the southeast and following the rooftops back towards the hole.

Zion National Park: (Honest Hearts Expansion)

Found in the general store in the northwestern part of Zion, on the bottom shelf of a broken cabinet behind the counter.

Big MT: (Old World Blues Expansion)

Found in the X-17 Meteorological Station, in the room on the catwalk next to the model houses.

Lonesome Road: (Lonesome Road Expansion)

Found at the Junction 7 Rest Stop just past the High Road. When leaving the High Road, take a right, the shop is at the bottom of the hill. The snow globe is upstairs, inside a fallen bookshelf.

All of the information in this guide was taken from Fallout Wiki. If anyone feels my reformatting and placing of this data here is out of line or infringing in anyway I am more than happy to remove this guide.