Battambang is best known for its Angkor-period ruins at Ek Phnom and Phnom Banan, but there's also Phnom Sampeau - the site of the local Killing Fields, and of course the norry - an innovative Khmer "vehicle" used for travelling along the creaking railways.
Although not on the main tourist route, but it will be worth a visit if you want a place to experience the real Cambodia.

An Angkor-type temple ruin, about 15 km north west of Battambang. The road goes alongside lovely small rivers bordered by trees and small villages and is in general a very nice area.

A good way to take in the countryside around Battambang is a ride on the bamboo train (called 'norry'). It is a unique and creative form of local transportation, consisting of a small motorcycle engine-powered bamboo cart that rides the railroad rails picking up and dropping off passengers, cargo, animals and motorcycles along the way.