Posture is a big thing with cycling. Ab and lower back exercises (e.g., crunches, low back extensions, side bends) are all good. For your upper body, you already realized that cycling can make it seems like you've been doing a push up for an hour. So, chest exercises like bench press, push ups, etc. are good. Those also work the front deltoid, which tends to get worked in cycling. Triceps exercises like triceps pushdowns are good.

Very important to not neglect the back, biceps and legs. You don't want a muscular imbalance. Rows and lat pulldowns are good for the back. Any kind of pushing exercise is good for the legs.

Probably the best all around exercise is squats. It works your entire leg plus engages your back and abs to help stablize the weight.

Kim