The provincial town of Sisophon is the capital of Banteay Meanchey and the last bigger town before/after Poipet. Well worth visiting is the mountain pagoda of Phnom Chanhchang on the western side of town.
The undisputed highlight of Banteay Meanchey province is the massive 'fortress of the cat' temple of Banteay Chhmar, which sees a very limited number of visitors and is a loveley place to indulge in local life and to experience a night or 2 in a homestay.
Often overlooked, Oddar Meanchey has old temples and sites of historical significance. Anlong Veng was a Khmer Rouge stronghold, and the remains of buildings and locations including Ta Mok's house and Pol Pot's grave can be visited. The Champei waterfall (Laang Ta Thong) is popular with local tourists.