I haven't swam since my son was born - havn't had the time - but if I had known how therapeutic it is for my neck and shoulders RSI I would have just swam instead of going to the chiropractor and physical therapist!
It works so well that if I swim before work I can work all day completely pain-free.
Besides just doing laps I do some stretching exercises - like I:
tread water and push my arms all around me in big circles around my body with my wrists flexed or extended.
do a bridge underwater - bend my knee and grab my foot behind me with my hand, and then do the same with the other foot (at the same time on really flexible days)
do a really slow butterfly stroke with my hips extended to feel a max stretch and pulling my arms as far behind me as they'll go
Swimming works even better than running and then doing yoga.