One way to assess competitiveness is the number of people who apply vs. who get interviewed; the ease of applying on AMCAS, however, dilutes this number.
Board pass rates generally correlate well with USMLE scores. A program with >90% pass rate will probably have applicants with high Step scores; one with <80% less so.
Programs do have an idea of the average resident's GPA and Step score. Will they tell you if you ask them? Dunno, but at some interviews they stated them.
Where have people at your school matched or are getting interviews at now? You can gauge your own application by their capabilities.
Very competitive programs are more likely require or highly suggest 1-2 years of research. If you look at a list of the programs with mandatory research, they correlate well with the most reputed institutions.
A list of where graduating chiefs go can help. Institutions that graduate chiefs who more often go directly into private practice may not emphasize your academic credentials as much. A place that has chiefs match into plastics, fellowships at Memorial Sloan Kettering, and have a history of making academic surgeons will want you to show you can do the same.
Finally, the more residents a program has, the more leeway they'll likely have in accepting someone who hasn't maxed out the applicant triathalon (Step, Research, GPA), i.e. someone with outstanding research but with a mediocre Step I. It just makes sense you'd have a better chance getting into a big program (>5 categoricals) vs. those who only take two.
To roughly do the 5 program thing...
Very competitive (not in any order, and just a sampling)
1. John Hopkins
2. MGH, Beth Israel, Brigham (the Harvard hospitals)
3. University of Washington
4. UCSF
5. University of Michigan
*I would include the best community programs (Virginia Mason in Seattle, Baylor Dallas) in this echelon
Average- hard to call any program perfectly average. Most have their +/-. For example, I wouldn't say it's easy to match at a big institution like Utah or North Carolina, even though people would not mention them in the Top 20 competitive programs. I don't think you can compare Rush vs. U of Miami vs. Arizona... you'll find a variety of applicants for them.
Easier matches
1. Carillion in Roanoke, VA (only unfilled program last match)
2. Texas Tech El Paso
3. some programs in New York City (you can find the whole spectrum of programs there)
4. Washington Hospital in D.C.
5. Tulane (I'm assuming after Katrina it would not be highly sought after)