For swimming strength (TI of course) because it's core a driven technique and not shoulder driven I do alot of core exercises using a ball. I also do yoga (spine alignment/flexibility) and Tia Chi (for more relaxation and breathing). I also do lat pull downs with light weights not for bulk but for strength.
As a triathlete I do some light wieght training more to benifit my run/bike part
I think above all I swim alot that is a huge benifit in itself.
What lies behind us and what lies before us are tiny matters compared to what lies within us.
Ralph Waldo Emerson