I have many, each one my own custom design representing something meaningful in my life. If you feel the need to ask others what to have then I would suggest not going ahead. However, if there is something of meaning to you then imagine a concept, tailor your very own design, and absolutely go ahead and do it. If, in the future, you don't like the tattoo, then you may at least still like it's meaning. Choose wisely - not off the wall in your local tattoo shop (unless the perfect one for you already exists there of course).
Be warned, as mentioned, they can become addictive.