Yes FREE themes are a great thing, if you are just getting started with WordPress. However if you are serious about your website, the best possible investment that you can do, is to get a Premium (paid) WordPress theme.
A professional theme will enable a whole new range of possibilities and save you a significant amount of time and money.
For the best WordPress themes, look no further than ThemeForest. We have been using it, for a few years and they offer by far the best collection of great WordPress themes, plugins and products. They have a great community of very knowledgeable members too.