1) Go here
and click "find it" without filling in any other information.
2) Scroll down past "Schools at a glance". 285 programs are listed. Clicking on one will get you to a pdf (or to a page, in which case, click the "view comprehensive details" button).
3) Click away.
Most of the pdfs will give some type of admissions info, like what the minimums and average scores are. Take the average scores info with a grain of salt, because they usually include both domestic and foreign students, and the latter often need significantly higher scores (e.g. at U Colorado, the difference on the physics GRE is 67 points). Some schools don't even require the physics GRE.
I don't know much about astrophysics -- my impression is that it's a small field and that will limit your choices. You should probably talk to a prof who can tell you about different programs. Having a small specialty may not be a bad thing. For example, one of my fellow majors wants to study space plasma physics. Not many schools do it, but it turns out that many of the schools that are good at it aren't as competitive more generally so they're easier to get in to.
For example, there are two profs here who do astrophysics stuff who are, in my understanding, pretty darn good (Caldwell
known for the Big Rip
, and Gleiser
who I saw in a history channel program
which also interviewed Brian Greene and some other big names, so he's got to have something going for him). Dartmouth's physics graduate program is not the most competitive (although they may hold a higher standard for cosmology types) -- you may have a good shot at getting in.
Anyhow, best of luck.