Here's a good article at About.com Business Majors about whether or not getting an MBA is a good return on the investment.

If you are an aspirant to one of the top MBA programs, you know that it is popular to question the worth of MBA programs. Let us take a look at the return that MBA programs can generate purely from a financial point of view. Here is an interesting finding of a study conducted by the Graduate Management Admission council in 2002. Overall, a graduate earned $48,000 before an MBA program and expected to earn $75,000 immediately after an MBA - a 56% increase. Of course, there will always be questions about the methodology of this survey and the merit of 'expected' salary. Nonetheless, it is common to find that candidates earn more in their first job post-MBA, than they did prior to the program.They also have a good listing and other information about online MBA's here.