A realistic looking eye I made in Blender 2.57 . I'm not really that happy with it but It'll go. I'm going to use it for the head model of DNA that I'm working on.
Unfortunately I don't know how to get the texture with the veins to start at the back of the eye instead of in the middle as it is doing now. Finding out how to make it took me far more time than to actually make it. It's easy and doesn't take to much time to make a realistic eye in blender 2.57, if you know how to make it...
The iris texture is from some photo of a yellow eye that I edited in gimp to make it more usable.

Ah right, the tutorial that I used to make it was from a older version of Blender which made it more diffecult to do in the new Blender 2.57 where all the buttons and all that are set in a different way. This tutorial: http://www.youtube.com/watch?v=Mnz4m7jrFzo