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Personally, I enjoyed the episode in which Lex Luthor is split in two (Ã la Good Kirk / Evil Kirk) by Black Kryptonite. Sure, it was a little over-acted, and Lana's character seems to be increasingly useless as the series progresses, but overall, enjoyable.
Here's a full list of the variety of Kryptonite colours. Yeah, I didn't think there was a Black K.