I thought about extending it a bit, after all, the light spectrum goes infra-red, visible, ultraviolet, x-ray... but the 'x-ray vision' doesn't really work like actually seeing in x-rays would... I also thought about making him able to hear radio waves... but that would require a lot of physiology differences from us, then again, you can cover a lot of ground with 'but he's Kryptonian'. It would also be really cool if he could selectively see different wavelengths, like these shots of our galaxy:
