Google IPO'd with a market cap around $23.1B which went up to $33B very quickly: http://www.google-ipo.com/

Google's revenue in 2004 was $3.1B: http://bit.ly/bOQZeZ

Facebook's revenue for 2010 is rumored between $1.2B and $2B: http://techcrunch.com/2010/03/03/facebook-revenue-2010/

VC investment rounds and secondary market transactions are probably not the best way to price a company, but they seem to be in the ballpark.