How can I get stronger wrists and hands?

After just completing the fb strong program, which I loved, I noticed that my hands and wrists are a weak link. I have relatively small hands and slender wrists compared to the rest of my body, and I had to drop my weights several times and lift lighter because I got cramps in my hands. My wrists might also be the reason why Iā€™m having trouble doing proper push ups. So my question is, are there any exercises that can improve the strength of hands and wrists?