Starting in December I have added core exercises and more indoor bike trainer workouts.
Core exercises have been self taught from books like these and others; Core performance essentials, Exercise balls for dummies, and Strength training on the ball. I have even replaced my office chair with an exercise ball. The biggest help I think I'm getting comes from the Cyclo-Core Off Season Conditioning DVD. The focus of the DVD is on Body Weight & Resistance Training workouts. It took 3 to 4 sessions before I could complete the exercises correctly.
Indoor bike trainer workouts consists of 3 days a week with 1 hour sessions using the 17 week schedule from http://fasttandem.com
I am feeling stronger and am looking forward to good race results this coming spring.