Bicycling Magazine published an article on Core workouts for cyclists. The article is called Get of your Ass and it can be found here. The workouts can be found out here.

Some of the suggested workouts are:

Plank

Single-leg step down:

Check the workouts out.

You can also check a series of videos from Selene Yeager, who is the fitness adviser for the magazine. The videos provide additional workouts to strengthen your core.

You can find about 9 videos of the workouts on this link.