I had been holding off posting because most of the things I would say have already been said. That said I can add a few thoughts.
Cross-spectrum does nice calibrations, and I and my friends have had good luck with their mics. I've also had good luck with the Dayton calibrated mics (specifically the umm-6), and Parts Express's Omnimic. I have used the Behringer mics in the past, but I cannot recommend buying a Behringer ECM8000 today, as their QC is not what it used to be. Generally, you should expect to pay at least $60-$80 dollars for a decent calibrated mic, which is where the Parts Express calibrated mics tend to hover.
USB mics are much more portable and convenient, and do not require phantom power, but you should know going in that they are somewhat limiting if you need to make very time-sensitive measurements from multiple sources. This is particularly true if you're trying to do crossover design or sub-woofer integration. For those kinds of applications, it can be very helpful to have one audio device for both input and output, which is impossible with a USB mic.
That said, there are workarounds for those issues, and if you don't have an interface with phantom-powered inputs already, then the USB mic will be a definite cost saver.