I know I'm not the only person here who has problems with white cycling tops turning yellow due to contact with sunscreen. Has anyone found a good solution for this?

Someone in a local cycling club suggested this, which I have not had a chance to try yet:

For sunscreen stained cycling jerseys: combine regular blue Dawn dishwashing liquid 50:50 with hydrogen peroxide. Soak for 10-15 minutes. You may have to rinse and re-soak, but usually a little rubbing on the tougher areas and you're done. This will NOT fade the colors. Rinse by hand really, really well -- do NOT put in your washer, as that much Dawn will foam out of your laundry room and into the neighbor's yard!