There's also Green Card PERM Salary data available on sites like http://visadoor.com.
H1B's typically have less years of experience compared to Green Card applications, even through both their titles might say Senior Software Engineer for example. If you are researching salaries, I would definitely look into PERM Salaries as well.
Glassdoor groups all the salaries reported for a title over the years in one bucket. Hence, I find the PERM and Labor data very helpful because you can see how salaries have changed over years.