Whole Foods (WFMI) faces challenging fundamentals in the gourmet grocery business. In its glory days, when Whole Foods was renowned for gobbling up whole paychecks, its stock traded at three times the current multiple of about 21 times 2010 earnings of 92 cents per share. While those profits represent a 27% rise over 2009, the shares looks expensive considering Whole Foods' geographic expansion and tough competition in a low-margin business. While the stock, at 1.7 times book value, is trading below the S&P average of two times, it is not producing free cash flow per share. "Whole Foods is a broken growth stock," says Lew Piantedosi, co-manager of the Eaton Vance Large-Cap Growth fund (EALCX). "I would not pay 20 times earnings for this company. It is not likely to have the growth profile going forward that it had in the past."

Investors may find peers more appealing than American Tower (AMT), the most mature and profitable of the public U.S. operators of broadcast and communications towers. It landed on our list by virtue of its 36 P/E based on estimated 2010 earnings of 87 cents per share, a 30% increase over 2009. Bulls see growth in rent revenue per tower and through international expansion. But American Tower is expanding in India and operates in Mexico and Brazil, so those prospects may already be baked into shares. Ed Maran, a portfolio manager of the Thornburg Value Fund (TVAFX), is willing to pay up for growth. But he owns less-profitable tower operator Crown Castle International (CCI). Using free-cash-flow metrics, another peer, SBA Communications (SBAC), is the cheapest of the bunch.

Investment-management giant T. Rowe Price (TROW) boasts a rich valuation that reflects success drawing in assets, especially to target-date retirement funds. But those only account for 10% of T. Rowe's total of about $270 billion under management -- still well below peak levels. True, T. Rowe has a competitive advantage in its pristine balance sheet, with over $1 billion in cash (including mutual-fund investments) and no debt. But operating margins are challenged, and investors probably shouldn't pay 24 times estimated 2010 earnings. On forward earnings, T. Rowe trades at a 90% premium to other asset managers' P/Es, but historically has traded at a 20% premium.

Iron Mountain (IRM) is a stock investors love to own in uncertain times: it is the dominant global player in record storage, and a majority of its business is recurring. It is producing free cash flow of 67 cents per share. But as the economy improves, and if Iron Mountain's revenue growth stays around 5%, it begins to look paltry, especially if expansion is hampered by debt. (Long-term debt to total capitalization is 63%.) In such a scenario, investors seeking growth may dump Iron Mountain, whose multiple of about 28 times 2010 earnings outstrips its projected 18% rise in profits.

Barron's was skeptical about Intuitive Surgical (ISRG) in a report last July ("Robot Dreams," July 28, 2008), when the dominant player in robotic-surgery devices traded at around 45 times forward estimates, topping another list of richly-priced S&P stocks. Intuitive shares have fallen from about $323 in late July 2008 to $163, but still look expensive at more than 27 times estimated 2010 earnings of $5.96. Just last summer, Wall Street was projecting the company could earn $8 or $9 per share over the next couple of years. The market for robots that perform surgeries isn't saturated, and hospitals are likely to boost orders as an economic recovery takes hold. But investors probably don't need to pay 27 times next year's earnings given the recent share performance.

Then there's Salesforce.com (CRM), which has produced steady earnings with software and "cloud computing" for customer-relationship management. But some analysts question its ability to continue boosting margins and free cash flow as it adds staff and expands internationally. At a lofty 49 times estimated 2010 earnings, the stock is still trading below the low end of its five-year range. But current multiples of earnings and cash flow show the stock is at least trading at fair value given its growth prospects, according to a KeyBanc analysis.

One tech name on our list, Juniper Networks (JNPR), boasts a multiple of nearly 26 times 2010 earnings. More than half of the analysts covering the provider of network infrastructure and related services have a Hold rating on the shares. Those offering a target price, on average, think the stock is worth about $21, which is 19% below the current price. One caveat: Barron's speculated in April that Hewlett-Packard (HPQ) may see Juniper as ripe for takeover.

We have to admit we liked three names that landed on our list. Amazon.com (AMZN) is trading at nearly 40 times estimated earnings for 2010. We wrote a positive cover story on the stock earlier this year ("The World's Best Retailer," March 30), and Amazon subsequently beat Wall Street earnings estimates and boosted operating margins. Its free cash flow is significant, at $3.17 per share, and analysts project continued profit strength. No surprise, it delivered one of the best 12-month share performances on our list. Amazon may just be eternally expensive: over the past five years, its median P/E is about 52, and it has traded as high as 130 times future per-share profits.