"The energy sector has been the U.S. stock market's best performer over the past three and five years -- and among the best so far in 2007," says Richard Moroney in his Upside newsletter.

He says, "Shares of energy companies, especially equipment and services concerns, seem unduly cheap -- even if per-barrel oil prices retreat by $10 or $15." Here he looks at Gardner Denver Inc. (NYSE: GDI) and NATCO Group Inc. (NYSE: NTG).

"Over the last three years, spending on capital expenditures has grown at an impressive 28% annual clip. Even if oil and gas prices drop sharply, which seems unlikely given supply and demand forecasts -- capital spending should remain robust.

"Gardner Denver is one of the largest providers of reciprocating pumps used in oil and gas drilling and production. For full-year 2007, management lifted its per-share profit guidance to a range of $3.10 to $3.18, up from the $2.49 earned in 2006. Gardner Denver, positioned to exceed consensus profit estimates, is a Best Buy.

What are the best energy investments for long-term investors? To answer this question, I surveyed 20 of the nation's leading financial newsletter advisors to find their current favorite ideas in the energy sector.

Interestingly, the advisors see the best opportunities in areas well beyond traditional oil firms; indeed, no one included in this report chose a major integrated oil company. Rather, the advisors have shown a preference for various oil services sectors, non-oil energy sources, and developing alternative technologies.

Some focus on areas such as deep-sea operations with Diamond Offshore Drilling Inc. (NYSE: DO), Transocean Inc. (NYSE: RIG) and Oceaneering International (NYSE: OII), while others look toward oil shippers such as Nordic American Tanker Shipping (NYSE: NAT) and refiners such as Valero Energy Corp. (NYSE: VLO).

Others chose companies that make specific products needed by the oil & gas industries such as NATCO Group Inc. (NYSE: NTG), which makes a wide range of oil & gas processing systems; Dresser-Rand Group Inc. (NYSE: DRC), a maker of control systems; Gardner Denver Inc. (NYSE: GDI), which makes compressor and fluid transfer systems; Tenaris (NYSE: TS), a maker of pipes and tublar products and Schlumberger Ltd. (NYSE: SLB), the largest and most diversified of the oil services companies.