I've been meaning to put up a little post about this for a while now and keep forgetting - so here it is!
If you have an iPhone, you need the Knit Buddy app. I have no affiliation with it's programmer, I just love it.
Knit Buddy is the best knitting app out there so far. It combines stash management, needle tracking, and project management in one app. Within project management you can set up and maintain customized, separate counters that will save when you close. In needle management - here's a screenshot of my needle list -
you can choose whether to use US or metric size (I choose metric -much more accurate! If you don't know the US to metric needle conversions I would highly recommend you train yourself to use the metric sizes for the benefit of your gauging). You can enter the type of needle (straight, circ, dpn, interchange), the material (wood, metal, plastic), the length, size, then you can flip a switch to show it is in use (the needles highlighted in yellow in my picture are in use), and even add a note. For me, the notes are essential b/c I have 20 million projects going at any given time and can never remember where all the needles are.
Here's a screen shot of the yarn area. You can enter all pertinent yarn info, take a picture, and it stores it by weight. I honestly don't use this or the project section very much. For me - this app is worth its weight in gold just for the needle organization.
You can find this app by searching in the App Store for Knit Buddy. It's written by David Ross and costs $2.99. There's also a Rav group for Knit Buddy users.