Been to Montenegro a few times and stayed at a hotel in Budva on one trip. The views from up in the hills are amazing. Personally I mostly like to loaf around the beach, the bars and the pizza places to be honest but the one place I'd characterise as a "must see" is the Njegos Mausoleum at Lovcen. We'll be back there again in September, Tivat this time.
Lake Skadar is nice as well, we went on a boat trip. You can see the cost of Albania in the distance.