There have been discussions here in the past about methods of storing circular needles. One of the challenges I find is how to label the sizes so that it's easy to get my hands on the correct size without a lot of hassle.
I just puchased these little plastic tags from patternworks.com. The tags fit onto the cable and are labeled in both US and metric. They slip snugly onto the cable and slide back and forth so in reality one wouldn't need to remove the tag when knitting. They do not have the needle length on them but that won't be a bother.
They come in 2 different sizes, from 0 - 6 and 7 - 35 US. The only needles I couldn't tag are the 00 and 000. Be aware that there are several tags for each size. I didn't know this and over-ordered. Not to worry as I'll send the extras to my best friend for his circulars.
I've put a photo here of the package along with one of my newly-tagged needles.