When I was playing Call of Duty 4: Modern Warfare on a regular basis a couple years back, we had a game clan member that had a signature quote in the clan forums that read: "A real friend is someone who bails you out of jail at 3am." I think that's kind of representative, but really the Cliff's Notes version.
I think real friends are the people that you can count on to be there as much as life allows them to, in both good times and bad. You can always count on them to do so, but should never abuse that faith and goodwill.
I think real friends are the ones that will use the influence and respect you give them in your life, not against you to shut you down when you're in the wrong, but -with- you, to help you improve yourself. You should listen to them; being able to trust someone you actually respect to tell you that you're wrong, and to help you become a better person is a rare gift.
I think real friends are the ones that don't see past or around your many flaws, but actually see your many flaws, and love you despite those flaws. They see the flaws, acknowledge and even accept them, but also see the part of you underneath those flaws that's worth hanging onto, even when you can't see it yourself. You should accept their unconditional love as graciously as possible, even when you can't see yourself as they see you.
I think real friends are the ones that will come to you and be there just to be around you, even when they don't want anything in return except the pleasure of your company, and to share experiences together. Real friends are the ones with whom comfortable silences are actually possible, because you're together in thought, even when no words are ready or even necessary.
I think real friends are the ones who would leave a gaping hole in your life if they were gone tomorrow. You should spend as much time with them as possible today, because we never know if there will be another tomorrow with the ones we love. If something, God forbid, ever happens to a real friend, you will want those lost times and opportunities back to do over. Since that won't be possible, do it right the first time.
I think real friends are worth sacrificing something of yourself for. The real friends will almost never ask it of you; but if they do, you'll know they really need it, because it won't be done lightly. If it's asked, you should be willing to give of yourself, as they've given to you by enriching your life.
I think real friends are both rare and precious, and worth savouring every second of time you are graced with aharing together.