There are seven snow globes in the base game (plus more in Old World Blues), each worth 2,000 caps when sold to Mr. House or Mr. New Vegas's collection. If you'd rather not hunt them all down, the console can add any snow globe straight to your inventory with player.additem and its base ID.
The command
Open the console with ~ (how to open the console), then add a snow globe by its base ID:
That adds the Nellis AFB snow globe. Every snow globe's base ID — and a ready-to-copy command — is on the snow globe IDs list.
Selling them
Snow globes are only worth caps if you turn them in: give them to Jane (Mr. House's securitron) on the Lucky 38 penthouse, or to Mr. House directly, for 2,000 caps each. Spawning them with the console still lets you cash them in the same way — an easy caps boost.