The special offers section on their website seems to be the best place in my experience. We've gone every winter for a night or two practically since they opened and I've always found booking direct to be the best deal.
As far as Great Wolf goes my older kids (10 & 14) like Kalahari better. The waterpark at Great Wolf is more little-kid friendly with fewer height-restricted slides, while Kalahari is better for older kids/adults with more big slides. Not that Great Wolf is bad - we sometimes do the smaller indoor waterpark resorts for DD3's sake and the big kids do enjoy it, but the waterpark at Kalahari keeps them amused for an entire weekend stay where the smaller waterparks leave them wanting to explore some of the other activities at the resort.