Oh, emma...Ravelry is the best (aside from KH, of course)! It allows you to input your stash - color, dye lots, number of skeins - track your projects and progress (or lack thereof in my case with some of them), organize patterns that you're working on, keep track of what and how many needles you have and even print off a little card of them to take with you to your LYS so you don't have to stand there wondering "do I have a size 10 1/2 circular in 16" or was it 32"?, and much MUCH more!
I just got my invite yesterday and spent the majority of last night entering my stash (still nowhere near being done) and just navigating the site. It's easy to get lost for hours but it's so worth it to have everything organized and in one place for a change.
If you want to sign up, go to www.ravelry.com and request to be put on the wait list. It took me about 4 weeks to get my invite which wasn't so long considering how long I've been living my yarn life in a chaotic state.