1 billion dollars visualized as... 1 billion dollars [google.com]. Or, in other words: one billion dollar is stacked on 12 standard palettes, together making up 10 Million $100 USD Notes. The artwork "One Billion Dollar" is not so much about what you see but what you could do (or not do) with the money.
It is also the most expensive piece of art ever made.
A similar, yet less expensive, recent work of the artist Michael Marcovici shows time as a heap of sand bags (same link, bottom of page). Each bag in the piece "The Rolex Time" is packed with 30kg of sand. Each bag lasts for 30 days in a standard "sandwatch". So, on the 18 palettes there are 972 bags with a total weight of 29,160 Kg. They would last for 81 years, which is about an average lifespan.
If you like comparing sizes, then check out The MegaPenny Project and Sizeasy. This work reminds me of Chris Jordan's "Running the Numbers" pieces, but then in physical space. Also see Demographical Data as Rice.
UPDATE: Google Sites has shut down the site for bandwidth reasons. Google? No bandwidth? Uh? Anyway, you can see the work here.