According to an article from Business on Sunday the most likely target is Nokia.
Cisco, the largest maker of Internet equipment is worth around $123 billion, while Nokia's market value is about $71 billion.
The paper said Cisco's mainstay networking market was fast changing with the convergence of fixed-line and wireless networks, and Cisco needed a merger to acquire the technology to create intelligent wireless applications, which Finnish-based Nokia could provide.More info at WashingtonPost