All multiple-joint exercises that involve the posterior chain (Hamstrings, Glutes, Hips, Legs, Erector Spinae & Lower back) pretty much the most powerful muscles used in Cycling.

Deadlift & Variations.
Squat & Variations.
Olympic Lifts & Variations.
Good-Mornings.
Lunges.
Glute Ham Raises.
Reverse-Hypers.

Also an abundance of core/abdominal exercises & upper body exercises for triceps, lats, back & delts.

Don't bulk too much, your looking to have the best relative strength possible.