F5 Networks was added today to the S&P 500 Index, joining an exclusive club of Washington companies already listed including Amazon, Costco, Expedia, Expeditors International, Microsoft, Nordstrom, PACCAR. Starbucks, Nordstrom, Plum Creek Timber and Weyerhaeuser. F5's shareprice has been on a tear boosted by the growing popularity of cloud computing. The company's shareprice soared by another 3 percent Friday, ending the day valued at a whopping $11.6 billion. Who might be next? Maybe Dendreon. The company, whose treatment for prostate cancer treatment recently received FDA approval, has seen its public valuation soar to nearly $6 billion, up more than 500 percent from just a couple of years ago.