Cycling has made the inner calves big and given my legs some cool looking veins, but the outer calf heads are puny. What are some good exercises to make my calves more symmetrical? Doing calf raises with free weights and toes pointed in might work, but I'm not sure about optimal weight, number of repetitions and frequency.

Walk up steep hills.
Walk on sandy beaches or through deep snow.

A good information source here:
Gastrocnemius
Calf Exercise Analyses
Periodization for Weight Training

Yes, it's a simple as walking. I used to do standing calf raises with 800 lbs on the bar, that will definitely do the trick. Now in my 50's it's pretty clear that it wasn't the best thing for my spine. The problem with weights and calf muscles is you either have to use insane weight or do 100's of reps in order to get any results. They are the densest muscles in the body.

I used to be a bodybuilder way back when, and could not develop my calves. It was a real struggle getting any sort of definition at all.

Then a few years later, I was off work for a couple months one winter, and wasn't cycling through the winter at that time, so I put on heavy boots and walked, and walked, and walked (mainly dropping off job applications, but sometimes walking just to get out of the house). It was a very snowy winter which added to the challenge of the walking. Come spring ... I had great calf muscles!! I could hardly believe it ... all that time in the gym and all I needed to do was walk.

For the past couple years, we have been living in a very hilly part of the world. All my walks include hills ... can't be helped! And again ... I'm pleasantly surprised by the calf muscle development.

I am guessing about walking in the sand ... we do some of that, but it is hard to tell whether it has contributed much. I'm just guessing it might have the same sort of effect as walking in snow.