There's been articles going around about kegel exercises and interestingly, I just had a conversation about kegels with my midwife today.
The best exercise you can do postpartum is not exactly kegels, but an exercise where you pull your belly button inward towards your spine. This is supposed to be done 500 times a day and can be broken up to not overdo it all at once. The motion is done quickly without a need to hold the position for any length of time. It can be done standing or lying down. It's basically just "sucking in your stomach". This has the benefit of also working your pelvic floor muscles and it helps bring back together the abdominal muscles that stretch during pregnancy.
Read both articles on the subject for yourself: