My proposed weekly workout cycle:
Day 1: Upper body.
Day 2: Legs.
Day 3: Core (or Pilates).
Day 4: Upper body.
Day 5: Cardio (swim/run/cycle).
Day 6: Yoga.
Day 7: Rest.
I'm pretty close to doing this now, but I haven't actually taken a yoga class yet. I think it would also be beneficial if I had a more strict routine. I'll revisit this cycle as The Relay (April 19) and the Chicago Triathlon (August 24) approach, shifting to more cardio and less strength training.