Not trying to go one-up on Pisa but Bologna has 2 leaning towers. Originally the wealthy families of Bologna had over 200 towers built during the mediaeval period of my-tower-is-bigger-than-your-tower, but wars, time and developments as well as bad subsoils has lead to a decrease in their number.

Torre degli Asinelli
Not for the faint hearted, claustrophobic or vertigo sufferers. The 498 steps to the top get narrower and as the 100m tower is also leaning by 1.4m it all adds to the tension. However for those that do make it to the top the views over the rooftops of the city are stunning. Open daily 09:00-18:00.
Garisenda
This is the shorter one at only 49m high but has a more extreme lean of 3m and is deemed too unstable to be opened to the public.