i thought this was pretty cool of them - the only one i really noticed during the episode was the green lantern/green arrow issue that was about red lantern/red arrow - but the giffen/dematis-era JL cover and the superman-instead-of-supergirl crisis cover, along with The Man of Steel Returns were great, too. [doesn't really look like giffen's art style, tho, does it? or at least not his usual inker/colorist - and the coloring is WAY too computerized for that era... although i guess the alterna-world does have a technological advantage over us, so maybe they got computer coloring a decade or two earlier.
the crisis cover looks spot on tho, doesn't it?]
i don't really get the significance of the black batman cover, though - is it supposed to be a refence to the doomsday-kills-superman issue or something? seems like they could have chosen something a little more iconic... plus - would alterna-peter have been around for that? i was operating on the assumption walter had kidnapped him a lot earlier than that, which took place during the 90's - the rest of the covers seem to be in the mid-late 80's. so something with the flash - in a green costume?! - might have been more appropriate, considering all the shakeups that book was going through, with the transition from barry allen to wally west.