Only 30 mins or so from Pisa via train or car, Lucca is great for a long weekend. It is a large town with so much history and yet not too many tourists. The old walls that surround Lucca are great for cycling around; it feels like you're in a park with groups of Italian old men sitting and chatting and joggers continuously lapping you.
Inside the city walls are a great number of piazzas, churches and even a huge tower with a tree at the top. The cafes and restaurants are reasonably priced and very relaxed. So, for a quick and well-priced get away with plenty to do, Lucca is a must visit.