There are a few supplements I know of that can encourage better hair growth, not exactly in magical Winx powers methods ha, but they are beneficial for the hair. If you take a daily vitamin it probably already has some of these supplements in them: biotin and niacin for sure. There are definitely other nutrients your hair needs to keep it healthy and encourage growth, but those two I always see when promoting hair growth.
I take a multivitamin every day, and sometimes a biotin tablet too on the side (along with calcium, fish oil, vitamin C etc). I don't think they necessarily speed up the growth of hair, but I take a few vitamins (because I know my body does not get everything I need from my diet) and it keeps my hair growing healthy. I'm fairly sure if I didn't have the right supplements it would grow poor, possibly even slowly.
I went through the exact thing you are going through right now, trying to grow my hair out. I started with my hair above my shoulders about 2 years ago and I've only gone in for trims every 3 or 4 months since. My hair is now about to the middle of my back which is pretty substantial. At first it felt like it was never going to get longer! But it finally hit me one day "Wow, it's getting longer!"
Some other natural (and probably obvious) tips are seen here:http://www.ehow.com/info_8210067_tips-stim...air-growth.html
Eat well (protein-- hair needs protein!), make sure you have all of your vitamins, no harsh chemical treatments, and trimming every so often.
Sometimes it's the trimming that holds my hair back from being as long as it could have been (usually I get an inch taken off), but at least the split ends aren't causing me to pull out my hair.
Good luck, though I think for the most part it is a waiting game. : )