there are some great ones, some ok ones and some horrid ones, just like public and private schools :-) it's nice they exist b/c they offer more choice.
google charter schools in whatever area you are in/going to be in and then check out their sites. some will have their charters available. if not, call them and have them pdf it to you. also ask about their state test scores, how they handle discipline, bullying, what is unique about their school, how long are their wait list, when does their lottery happen, how involved are parents, what is their financial situation look like right now, what other services do they offer (school lunch, buses, before/aftercare, etc) and any other questions that might be important to you.
if you already live here you will hear parents talk about the different ones. if not, maybe ask the school if parents involved with their parent organizations are willing to speak with you...