Also on these boards
little foam things called "marshmallows"--get them at Michaels. Heat them, press into texture, and you have an instant stamp.
I always make my own stamps or find something unique to stamp with. Typically I use craft foam and cut out shapes and carve into the foam with a wood burning tool. I have found that craft foam is cheap, durable and really great to use with fabric ink and paint. In addition I always try and find unique object or simple things that I can use as a stamps to repeat pattern across the surface of fabric.