"Warren Buffett's Berkshire Hathaway revealed a new position in Nalco Holding (NYSE: NLC); it's my favorite pure play on water filtration," says Chris Mayer in Daily Wealth.

"With a $1.6 billion market cap, Nalco is a small-cap stock, but it's actually one of the world's largest water-treatment companies. Customers use Nalco's products and services to prevent corrosion, contamination, and the buildup of harmful deposits.

"Buffett picked up 8.7 million shares. That makes Berkshire the second-largest shareholder in the company, with a little more than 6% of the shares.It's easy to see what Buffett likes.

Last December, over 100 stocks were featured in our Top Picks for 2007 report. Now, at mid-year, we turn to the 20 advisors whose picks showed the strongest gains to get an update on their previous picks, as well as a new favorite stock for the second half of the year.

Chris Mayer, editor of Capital & Crisis, chose Rosetta Resources Inc. (NASDAQ: ROSE) as his top pick for 2007. The stock rose 32%, as of June 1, 2007. Here is Chris's original recommendation for Rosetta and his new favorite stock for the rest of 2007.

Updating Rosetta, the advisor now says, "I continue to like ROSE, which should increase production greatly this year. The company is in good financial shape. It still has a relatively low-risk portfolio of drilling projects.

"I also feel good about the future of natural gas prices. In a world where we're draining the conventional natural gas wells at a fast rate, large fields of relatively untapped gas potential in the lower 48 are going to be worth a lot. Rosetta has that in its Rio Vista interests.

The company also keeps blowing away estimates. In the March quarter, earnings came in 33% better than analysts expected. In December, they beat the consensus by 24%. All of this and it still trades for a reasonable multiple -- only 14 times next year's (too low) estimate."

Each year Steven Halpern, editor of TheStockAdvisors.com, surveys the leading financial newsletter advisors asking for their favorite stocks for the coming year. This article is part of his 24th annual Top Picks Report.

Rosetta Resources, Inc. (NASDAQ: ROSE) is the top speculative pick for 2007 from Chris Mayer, editor of Capital & Crisis. He explains, "Rosetta is primarily a gas exploration and production company; the vast majority (87%) of its gas reserves is in the Sacramento Basin and south Texas. The rest is in the Gulf of Mexico and the Rocky Mountains.

"This is no small matter. Earlier in 2006, Bolivian President Evo Morales sent his army to seize Bolivia's natural gas fields. While North American producers incur higher costs of production, they come with the added safety of having their properties safely tucked away in the United States.

"Rosetta has the opportunity to vastly increase production and add significantly to reserves. Next year alone, we could see a 40% increase in production. Earnings could double to $2 per share, assuming average gas prices of $8 (in 2006, average realized gas prices were about $7.37). Based on that 2007 estimate, the shares go for less than 9 times earnings. By 2008, total production could nearly double from 2005.

"Rosetta has ample and long-lived gas reserves. On a net asset value (NAV) basis, using only proven reserves of 359 billion cubic feet equivalent (bcfe) and assuming an average gas price of $8, I estimate NAV at $25 per share. Based on a recent price of nearly $18, the company trades at about 30% discount to NAV.

Each year Steven Halpern, editor of TheStockAdvisors.com, surveys the leading financial newsletter advisors asking for their favorite stocks for the coming year. This article is part of his 24th annual Top Picks Report.

Six Flags (NYSE: SIX) is the top conservative investment idea for 2007 from Chris Mayer, editor of Capital & Crisis. The advisor notes, "Six Flags is a great brand name, and about 34 million people visited its amusement and water parks last year. And they all come and spend money.

"Dan Snyder, the whiz-bang executive who made billions with Snyder Communications, took control of the company last November. He's also the guy who bought the Washington Redskins. In the time he's owned the Redskins, profits have tripled, and it's now the most valuable property in the NFL.

"One of the first things he did was hire Mark Shapiro to run the show at Six Flags. Shapiro was the No. 2 guy at ESPN. So he knows a few things about marketing and building up a media asset. Since he's joined Six Flags, he's brought on a bunch of executives and operators from ESPN and Disney.