Forgive me for making my obligatory "stretching/flexibility is over-rated" post, but it's a point worth making if you are just starting out.
In the same way that it can be a temptation to spend money on books and DVDs and stuff in an effort to get better sooner, trying to improve your strength/cardio/flexibility in order to get better at jiu jitsu is almost a waste of time.
Until and unless you start competing, don't worry about your cardio--it will get better as you start to train. Same with strength training.
Flexibility is even less important. Unless you are genetically stiff, a good warm-up will prepare your muscles for all the flexibility they need. A truly effective warrm-up doesn't mean Navy SEAL workouts, it means getting to the point where you feel more comfortable moving than standing still.
Exceptional flexibility is not a main characteristic of any of the top jiu jitsu fighters out there: Roger, Jacare, Marcelo, Rani, Drysdale, Xande, Leo, Lovato Jr., Fowler ... It's worth remembering ...
That said, here is my favorite website for stretching. Click on the part of the body you want to stretch and look on the right-hand side of the table for the various stretches.
http://www.exrx.net/Lists/WtMale.html