Half Price Books said today it has launched HPB.com, which features its new online web store, HPB Marketplace. Through a partnership with Monsoon Commerce Solutions, a company that powers websites for online retailers, Half Price Books has begun selling books, music and media online. The company says its website will give users access to more than 120 million book, movie and, music titles sold through Half Price Books and other independent sellers. Previously the company offered its inventory via third- party sellers such as Amazon and Half.com.