dbl overhand static holds or pulls is a great way to build grip strength. i also do db shrugs with no straps to help build grip. 150's are the biggest we have and i can hold them for sets of 15 no prob.
http://video.google.com/videoplay?docid=7354803557310854786&hl=en
http://video.google.com/videoplay?docid=7354803557310854786&hl=en