Monday was an up-and-down day on Wall Street, as major stock market benchmarks moved on both sides of unchanged before settling down on the day. Biotech stocks weighed especially hard on the Nasdaq, but that didn't keep some stocks from scoring impressive gains. Herbalife (NYSE:HLF), Steel Partners Holdings (NYSE:SPLP), and Achillion Pharmaceuticals (NASDAQ:ACHN) were among the biggest winners today.

Herbalife gained 7% as activist investor Carl Icahn gained control of three more director seats on the multi-level marketing company's board. With an investigation into the company's practices having recently begun, Herbalife stock is well off its highs as fearful investors worry that the company could have its business model threatened. Yet Icahn remains optimistic that Herbalife represents a solid value and has plenty of growth potential ahead. Moreover, Herbalife also likely gained from news that peer Nu Skin Enterprises (NYSE:NUS) avoided the brunt of potential damage from Chinese regulators, paying fines of less than $1 million in connection with its practices in the emerging-market nation.

Steel Partners Holdings rose 8% after the limited partnership announced that it would buy up to $49 million worth of its partnership units in a Dutch auction. The holding company is an interesting conglomeration of businesses in different industries, ranging from a combination well-completion and sports-services company to hot-dog giant Nathan's Famous, and it has historically traded at a value well below the sum total of its holdings. With the Dutch-auction tender offer, Steel Partners is aiming to boost its unit price while also giving it a chance to buy back partnership units at an attractive valuation.

Achillion Pharmaceuticals rose 7% after the biotech company got an upgrade from Maxim Group. The maker of the once-promising hepatitis-C treatment sovaprevir got crushed last fall, when the FDA chose not to lift a clinical hold on the drug that the agency had originally imposed earlier last year. Yet after that big drop, some believe that unlike other high-flying biotech stocks, Achillion represents a reasonable value at current prices. There's still plenty of risk given Achillion's historical inability to get promising treatments all the way through clinical trials, but with the stock down, analysts see it as a worthwhile gamble.

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