Just knowing that you know what graduate school is really like, and the fact that you have proven research experience higher than the little projects undergrads do (I'm assuming here that you have a MS with thesis), you are a very attractive candidate for a PhD program. The size of the graduating class from any PhD is so much smaller than the matriculating class because most undergrads don't really know much about the graduate student life. They often get bored, or depressed or just impatient with all the hard work for such little pay. So yeah, since you know what grad school is like and are willing to go through it again shows that you must really like doing research and are not likely to drop out midway. I'm in the same position as you are, and I've talked to a few of my profs. They told me that I have a good chance of getting into any program in the country. And it will help you even more if you can take the Subject GRE and get anything above a 50th percentile. I think your chances are quite good.
And since you have done research, you should have some idea of what you want to do in terms of research for your PhD. So read professors' research papers and email them about it. Ask to meet them if the school isn't too far away. Then if they do invite you, definitely go visit. It will help your case a lot if you can make a good impression (i.e. know what you are talking about, are able to fluently discuss your research, your career aims etc.)