Shanghai is the one largest city in China and has the most sky scrapers of the world. There is so much to see and to visit, I'm a big fan of this city.
If you want to see something of Shanghai, then actually a city tour is a must. Of course it is up to yourself what you want to visit. My city tour consisted of the following sightseeings.
The Buddha Tempel
Near the Yu Garden
The Bund
See also my previous posts about Shanghai:
Shanghai by night #2 - Famous shopping street Nanjing Road
Shanghai by night #1 - View from the Jinmao Tower
The Bund in Shanghai by night
The Bund in Shanghai by daylight