How Can I Keep my Hair Untangled During the Day?

I have rather long and thin hair, and even if i wash and condition my hair well, and brush it thoroughly before and after I sleep, my hair just gets tangled during the day. It gets really annoying and knotty, and I was just wondering if there are any products or tricks to keeping your hair untangled during the day. (Oh, and I don't really like my hair up or in braids or anything, I prefer it down)