I've been to Pisa 4 or 5 times. I climbed the tower as a tourist (first time!) and then later as a guide, when I took friends and family. The Tower costs 17 Euro to climb and in season you probably should buy in advance as a limited amount of folks are allowed up each 20 minute period.
I agree with Larry - if you're in the neighborhood you must see the tower, and if you're there, it's an incredible landmark to climb! The climb is not the easiest due to the angle of tower and the worn marble steps. But it's breath-taking and rewarding once you get to the top.
I found Pisa to be a charming town, yet a small town. We spent some time on our last trip seeing the back streets and thoroughly enjoyed getting off the tourist path. Other than the tower area there are not many other "tourist spots."
The bus system is good, the shopping has a small town flavor, but you have to leave the Campo dei Miracoli ("Field of Miracles") to see it! Good luck!
Ciao,
Ron