The score you need greatly depends on the universities and programs you're applying to as well as how strong the other aspects of your application are. Schools usually post the averages of the accepted students on their admissions page. Often times these will also differ depending on the major - for example, if you are applying to a Physics PhD program your quant score will be more important than verbal. Also, more competitive or impacted majors would require a higher score to get accepted than other programs within the same school. So always be sure to check the admissions page for you specific program!
If you can't find any information on the required scores on a school's website, you can always contact them directly. They answer questions like that all the time, so it's completely reasonable and appropriate to ask them that :)
Finally, you can find average GRE scores for major universities (Harvard, Berkeley, UCLA, etc) and fields of study (engineering, humanities, etc) here: