Central St or better known as Zhong Yang Da Jie is the main shopping district in Harbin. This is where the buildings are a pretty sight because of its Russian influence. It is a long street of little eateries, restaurants (both Chinese and Russian), souvenir shops, cafes and what have you. Basically, if you are a foodie you will love this street. Personally, I didn't get sick of walking this street even though I visited it almost every day during my stay in Harbin.
Song Hua River
During winter, the Song Hua River will freeze and it transforms into a winter playground. There are numerous paid winter activities that you can play. For example, dog sledding, slide, ice skating, ride on a horse carriage. My personal favourite was riding on the horse carriage. Be sure to bargain if you are planning on trying on any of its activities especially if you are a foreigner because the locals tend to jack up the prices. There is no entrance fee to get into the area but if you are participating in its winter activities, you will have to pay for it.