Picking a Graduate School
You will want to go on the web and look at the web sites of a lot of schools. You want to find a school with faculty who are working on projects that interest you. (Try to avoid going to a school that has only one faculty member who is doing interesting things-- what if you don't get along?) You are going to be working closely on a project with some faculty member for quite a while, so you want to find a good fit. Many schools prefer that you not contact the faculty (by email or phone) until after you have been admitted, but they all DEFINITELY want you to have looked over their web sites. Many of the schools would like you to list the faculty whose areas interest you.
Purdue hosts the Big 10+ Grad School Expo at their campus in September. (9/24 this year.) A large number of good schools attend, and there are also some workshops that might be useful.
What about reputation? U.S. News ranks graduate schools in mechanical engineering as well as those other U.S. News rankings you might have heard mentioned. The list by discipline only goes about 4 deep in the free version, but the detailed version (which costs about $15) ranks about 100 of them. The ranked list is here. Like any rankings you should treat them skeptically, but they will give you the idea. Purdue is a good school, but University of Nebraska is not so good. (It didn't make the list.) There are other rankings too, such as the ones done sporadically by the National Academy of Sciences or the customizable rankings at PhDs.org. (Some of our students have found the customizable rankings quite a bit more useful than the U.S. News rankings.)
But will you get in? And will you get funded by them? Schools fund their top students first, so clearly the idea is to be one of the best students they will admit. From the U.S. News data you can make some really interesting graphs about the average GRE scores (Quantitative, Verbal, and Analytical Writing) that schools claim for their incoming M.S. students. (Caveat-- the rankings are specific to ME but the GRE scores are across all engineering programs at a given school.) Notice that everybody has a high Quantitative score, and that the highest Verbal score doesn't overlap the lowest Quantitive. The Analytical is the writing part, and every school reports an average higher than 3.7. Many times, schools will give some indication on their web sites of what it takes to get in and get funded. (Georgia Tech, for instance, would like to see GPA > 3.7, GRE V>=600 Q>=700 A >=5 for students they are going to fund.)