Once again, XtremeMac has added an interesting twist or two to a case design we wouldn't otherwise have much of: Verona Flip is sold in separate versions for the iPod nano ($25), iPod classic ($30), and iPod touch ($30), each folding closed in a horizontal book-like orientation. The iPod nano version is interesting only in colors -- there's a patch of additional tones to offset each basic case design -- and the included carabiner hook, while the iPod…