To me the word "crossover" pretty much means a Burley/Latakia mix -- especially with some Virginia added. I personally don't think Burley's, especially mixes of air and fired cured, need Latakia to create a campfire-smoke/leathery/salty taste profile. But each to his own. It only takes an additional dash of Oriental to merit the more common term, "American English".
I tend to avoid Latakia these days, but I have sampled C&D's Morley's Best, and IRC's Dr. Bradley. These are two somewhat different blends that both satisfy my definition of a crossover.
Both of these blends wore heavily on my palate, and I couldn't smoke much more than a couple of ounces. Dr. Bradley has been compared to Altadis' Count Pulaski. I thought Dr. Bradley had some really subtle floral notes that made it very interesting -- but again, as I said, 7 oz. was a bit too much for me. If memory serves, someone compared it to one of the McClelland Frog Morton blends, but I don't know which.
I'd really like to get Russ Ouellette's take on the topic of crossovers and American Englishes. Maybe Kevin can twist his arm.