There are no real highlights for tourists in Sapporo - none of the temples and shrines of Kyoto or old castles and residential districts.Although for those who have never been to Japan you could visit the Maruyama park area where Hokkaido Shrine is located.Likewise at the southern end of Nakajima Park there is another shrine complex.
Sapporo is a convenient place to stroll around and look at shops, enjoy the growing cafe culture and great restaurants.
Also Odori, Nakajima and Maruyama parks are all places to relax and view the changing seasons.Odori is a good place to do some people watching-it seems to attract various groups and individuals and is home to numerous matsuri(festivals) and events,including the Yuki (Snow)Matsuri in first week of February and the lively Beer Festival which sees block after block of beer gardens set up for a 3 week period. In between Odori and Maruyama you can find the Modern Art Museum and Governor's ex-residence and parkland -also worth a quick visit.
Quick Tips:
These days some JR stations offer reasonably priced bicycle rental too- Sapporo is pretty flat and riding a bike is a great way to get around. I recommended heading down to the Toyohira River where you can find a great bicycle/running track-head down river and you can almost make it to the coast. Within 15 minutes or so of easy riding you are out of the city.
A bit further will take you within an easy side cycle to Morei Park (on left hand side of river) whic is an architecturally designed park located in the middle of an old oxbow lake- this is a great place to spend a nice day relaxing on the lawns, checking out the various play areas and climbing the artificial hills for a great view.
In winter you could practice your ski/snowboard jumping here - a cheap alternative to visiting ski-hills.You can find a pamphlet in English at the tourist information centre in JR Sapporo.
Then if you head up river you can make your way to the outer suburb of Makomanai-site of various Winter Olympic facilities and again some nice park areas.
Best Way To Get Around:
Rent a bicycle or walk, but for lazier souls, the public transport is easy to use and convenient, especially in the slippery winter months. A trip on the SHIDEN (tram) can take you from the city to the foot of Mt. Moiwa, where the hour or so hike winds up through some nice old-growth forest to the summit. On top of Moiwa are several restaurants.