You are an excellent candidate.
The lack of any publications does not help. but if you have any poster presentations or others, etc, that helps make up for it.
Good recommendation letters are key. That writing score nobody really looks at. It is not a technical writing test, so it is worthless in the science fields.
I would say apply everywhere and anywhere you can. Go ahead and apply to places like MIT and Berkley (IF there is more than 1 person there doing research you are interested in!). I would say apply to 5-6 top tier schools and a couple of middle tier schools as well. Remember, the ranking is nice and impressive sounding, but it means nothing to what type of education you will get and how you will enjoy your experience. Those who hate the research they do and the person they work for hate graduate school; those who enjoy the research and the person they work for consider it the best years of their life.