Analysts are weighing in today on natural gas stock Clean Energy Fuels Corp. (NASDAQ:CLNE - 14.35), software concern CommVault Systems, Inc. (NASDAQ:CVLT - 47.20), and PC graphics company Nvidia Corporation (NASDAQ:NVDA - 13.14). Here's a quick roundup of today's newest brokerage ratings.

• CLNE was initiated with a "buy" rating and $18 price target at Capstone, pushing the stock fractionally higher ahead of the bell. The shares are down sharply from their March high of $24.75, but CLNE is still resting on a healthy year-to-date gain of 15.2%. Most analysts remain leery of the alternative fuel firm, though, with seven brokerage firms out of nine offering up a "hold" or "sell" recommendation.
  
  
• Goldman Sachs resumed coverage of CVLT with a "buy" rating, with the brokerage firm apparently enticed by the stock's recent pullback to support at its 10-month moving average. This long-term trendline hasn't been breached on a monthly closing basis since last September. CVLT is up 10.5% so far in 2012 -- and with a healthy 5.7% of its float sold short, today's bullish nod from Goldman could help the stock extend its year-to-date advance.
  
  
• Lazard Capital started NVDA at "neutral," and the stock is off 0.6% in electronic trading on the heels of this lukewarm note. NVDA is down 16.5% over the past 52 weeks, and the equity's latest rally attempt was thwarted by its looming 80-day moving average. With 15 analysts considering the shares worthy of a "buy" or better endorsement, a continued slump on the charts could translate into future downgrades.