Posemaniacs is a p good site for learning poses and studying muscles but I always found the poses themselves to be really 'stiff' looking. It's good to use in conjunction with gesture drawing, drawing from life, and what not - but on its own I can't really recommend it unless you want your drawings to look stiff.
Theres are other websites that have the 30 second gesture study too! off the top of my head, theres http://artists.pixelovely.com/ which has the choice of hands/feet, models, animals, and faces. it uses photos of real people too so there isn't an issue of the pose looking stiff and lifeless. it also has the option of giving you like 10 second pictures to 'warm up' and gradually lengthen the time, as if you were in a classroom.