According to eMarketer it's going to be $152.1 billion this year. The full report is available here: http://www.emarketer.com/Reports...

 
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I generally use the US Census Bureau to get an idea of E-commerce sales in the US.  It's free, accurate, and defensible. http://www.census.gov/retail/

Here are the numbers from Forrester's US Online Retail Forecast (Feb 2011). Josh Yang from Harvard Business School posted these figures (plus a lot more valuable data and thoughts) in his Ecommerce Landscape 2012 slide deck on slideshare (slide 6). E-commerce Landscape 2012

It's unclear whether these numbers include travel, digital downloads, and/or event tickets, but they are slightly higher than the numbers Tobias Lutke posted from Emarketer. I imagine these numbers include the entire US e-commerce market, ie all items purchased online.

but the graph says NOT INCLUDING TRAVEL, DIGITAL DOWNLOADS AND EVENT TICKETS. The question seems to be asking for another number which includes these segments.