Granada is known around the world for its high-quality rocking chairs which can be seen all around town. The main vendors a bit out of town on the road to Masaya.
If you want to go cheaper, there's the option to buy local and famous Nicaraguan pottery, which you can buy in town very nice choice: Dona Conchy's, a restaurant which also has a little sweet store in the back, where they sell very nice pottery, handmade by the owner, but the better option is to go to Masaya where there's a bigger choice and the prices are lower.
Also very typical are the hammocks, there are tons of hammock stores and factories in Masaya, but you can also get them in town for a bit more money.