I only buy rubberized cases and white does get a bit dingy with a grey tint, but I usually take a Mr. Clean Magic Eraser to them and they look brand new. I know you don't need suggestions but I really like this one:

http://www.amazon.com/STM-Opera-Case-iPhone-Packaging/dp/B008YRIY9A/ref=cm_cr_pr_product_top

I used to like clear cases so you could see the phone, but those are made of a different shiny rubber material and they turn yellow over time and you can't clean them.