Buy yourself a pretty ring. Buy ten if you have to. I bit my nails til they bled for twenty-two years until I got engaged. When I saw my beautiful diamond ring on ragged fingers, I was so ashamed and disgusted that I quit and haven't bit since. Buy yourself a nice ring, and every time you go to bite your nails, look at it and remember the money you spent on it and how unattractive it will look on your hand if you bite your nails. Good luck!
P.S. I tried all that other stuff, too, including the gum and candy, special nail polishes, the rubberband around my wrist, you name it. None of it worked til I got the ring. Once I did, I found that the nasty-tasting nail polish (that had not worked alone) helped to remind me if I put my finger in my mouth. Then, I'd look at the ring while tasting sour chili-pepper nail polish, and I'd never want to chew my fingers again!! It also helps to keep any ragged edges filed smooth so that they don't catch on anything. If they do, your temptation to bite the edge will quadruple!! Also, I'd stay away from the acrylic nails. I know some people swear by them, but they tear up your natural nails which don't seem to grow much underneath. Half the battle against biting is getting some length to your natural nails. If they start to look nice and get some length, you'll be less tempted to bite them.
P.S.S. I found something that REALLY helped me came in the form of support from my fiance. I waited until I went about a week without biting them, and then I told him that I was trying to quit biting, and he said he was so proud of me for trying. (I waited a week so that there wouldn't be too much pressure on me if I slipped and bit them and had to start over.) Then, about every other day, he'd look at my fingers and tell me how nice they looked, how slender my hands looked, and how beautiful my ring was. Even when I slipped, he'd compliment my other fingers and talk about how proud he was of each nail. I haven't bit them in such a long time, but he still keeps up the compliments! I know it sounds corny, but this encouragement, praise, and support really helped me. Decide you're going to quit, stop biting for a few days (the first few are the hardest), and then ask your husband for his support. Chances are he'll be happy to help you! Good luck!