A black IPA is just a hoppy black ale. IPA is shorthand for hoppiness, innit.
To be fair, I'm more of a fan of the actual pale ales rather than dark ones. My favourite styles are session IPAs and saisons. For a session IPA, you can't improve on Bullfinch's Rascal (they've run out, partly I suspect my fault, but they're brewing some more) and Burning Sky's Arise. Actually, both breweries do a fabulous range. Brew by Numbers are doing a fabulously murky pale ale at the moment. Well, it's more opaque than pale. If you did a wee that murky you'd be on the market for two new kidneys. Oddly, even Brewdog have yet to commission me to write copy for them.