* Biotech stocks edge up, continuing recent rally
* Best Buy tumbles after results, DSW higher
* Digital Ally gains before bell, has tripled this month
* Futures up: Dow 24 pts, S&P 2.5 pts, Nasdaq 7.25 pts (Updates prices, adds DSW results)
By Ryan Vlastelica
NEW YORK, Aug 26 U.S. stock index futures pointed to very slight gains at the open on Tuesday, with investors finding few reasons to buy after a rally in the previous session that took the S&P 500 index above 2,000 for the first time.
* The benchmark S&P failed to hold that level Monday, but ended at a new closing high. Equities have rallied lately, with the Dow and S&P advancing in seven of the last 10 sessions, and the Nasdaq climbing in eight.
* That momentum is still considered intact, and the S&P's price-to-earnings ratio is within historical norms, leading many analysts to believe the market is not overvalued. Nonetheless, further gains may be a challenge without positive catalysts and amid potential headwinds such as a reduction in Federal Reserve stimulus and a simmering conflict between Ukraine and Russia.
* Much of the market's recent gains have come on low volume, suggesting many traders may be reluctant to jump in at current levels.
* Among Tuesday's biggest premarket movers, Best Buy Co Inc reported second-quarter revenue that missed expectations and forecast a drop in same-store sales in the second half of the year. Its shares fell 3 percent in premarket trading. DSW Inc rose 11 percent in premarket trading after its adjusted earnings topped forecasts.
* S&P 500 e-mini futures rose 2.5 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average e-mini futures added 24 points and Nasdaq 100 e-mini futures added 7.25 points.
* Biotechnology stocks were among the biggest drivers during Monday's rally. That appeared to continue Tuesday, with Kite Pharma Inc up 18 percent to $26.38 after positive results in an early-stage study for an experimental cancer immunotherapy. Achillion Pharmaceuticals was up 4.8 percent to $11.30 before the opening bell. Gilead Sciences Inc rose 0.9 percent to $108.37.
* Digital Ally Inc jumped 12 percent to $14.01 in premarket trading, extending a recent surge that has seen shares of the wearable camera maker more than triple this month alone. The recent fatal police shooting of an unarmed black teenager in Missouri has fueled interest in the company's devices. The stock was one of the Nasdaq's heaviest premarket movers.
* Amazon.com Inc late Monday agreed to buy the live-streaming gaming network Twitch Interactive for about $970 million in cash. Shares rose 0.7 percent to $336.50.
* Durable goods jumped 22.6 percent in July, the biggest gain on record, though the number was skewed by strong international demand for aircraft. Excluding transportation, orders fell 0.8 percent. (Editing by Bernadette Baum)