MBIA, an insurer of mortgage securities and other financial products, is up more than 60 percent this year. The company, which almost went under during the financial crisis, is up 20 percent this week alone.
Based on a search of all U.S. stocks with a market value above $2 billion, Netflix is the biggest winner of 2013 so far, with the price doubling on a wave of enthusiasm about new distribution deals and its own original content.
"They have a long way to go to justify this valuation," said Michael Pachter, a Netflix analyst for Wedbush Securities. "This is a worse company than it was two years ago."
(Read More: Netflix 'A Worse Company Today': Michael Pachter)
Troubled retailer Best Buy is up more than 60 percent this year on the hopes of a turnaround or a buyout. Zynga shares have posted a 50 percent jump in 2013 after Nevada and New Jersey legalized online gaming, a market for which the game-maker is trying to become the interface in those states.
To be sure, not all investors believe the buying of these so-called riskier names are a sign of a last gasp for the bull market.
"To me, it's a sign of the early phase of another run because this is where people go first for beta," said Stephen Weiss of Short Hills Capital. "Plus, Best Buy is a classic early-cycle, consumer stock."
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