Im not sure how this would be determined, but I would like to see an expansive list. A quick google search turned up little.
Obviously a list would look at number of attorneys, but there are lots of intagibles that could make "smaller" markets easily compete with a city like DC. A friend was telling me that Houston has one of the largest legal markets in the country. I think he said it was top five. At first, I thought that seemed crazy and then the more I thought about it, I could come up with a whole host of reasons why that could be possible.
I'd also like to see where cities in the 200,000-800,000 population rank.