Most of the notebooks with long battery life are ultra-slim laptops. Other than Apple MacBook laptops (their battery can last up to 7 hours), there are very few full-featured laptops with good battery life. Apple MacBook laptops make use of lithium-polymer batteries (as opposed to the common lithium ion).
Ultra-slim notebooks on the other hand were able to have great battery life spans thanks to their energy efficient processors. At the moment Asus, Toshiba and Acer are the leading brands (Windows based) when it comes to long battery lifespan. The other major laptop brands don't seem too interested in producing such models.
Asus UL Laptops: Currently, the Asus UL notebook series have been making waves in the laptop market. They have gorgeous designs and are very fun to use. The batteries on these laptops can last anything from 7 to 12 hours on a single charge. One of the hottest models from this series is the 13.3-inch Asus UL30A-X5 laptop model.
Toshiba Satellite T135/T115: Another popular notebook series is the Toshiba Satellite T135 and T115 laptop series. All of the laptops from this range also have very impressive battery life. The T135-S1310 for instance can last up to 9+ hours on a single charge. Most of the casings on the laptops in this series have glossy finishes. The have very stylish side profiles and are also very affordable.
Acer Aspire Timeline: The Acer Timeline series is also another laptop series with long battery life spans. Although they are not as popular as the Toshiba and Asus laptops, they still hold their ground well thanks to their competitive pricing. Most of the Acer Timeline laptops have at least 8 hours of battery life.