If you've decided grad school is for you, then the next most important decision is where to go.
First, once you've found out what kind of physics you're interested in, locate the top people in the field and where they are located. Making a personal connection with a faculty member is a good way to get your application noticed. Do your research so you can make a good impression when contacting potential research advisors.
If you are less sure of your future research area, or are just looking for ideas, the following sources can help you assess the quality and resources available at different institutions.
All rankings should be taken with a grain of salt, especially since rankings are typically given in aggregate, and an institution might have a significant strength or weakness in your area of interest compared to its overall quality.