Both the Comixology apps (Comics, Marvel, DC, Image, etc.) and the Marvel Comics inside iBooks are *gorgeous*. I have Absolute Sandman, Dark Knight, Watchman, Planetary, etc. and a bunch of Marvel Hardcovers sitting on my shelf here and the iPad versions are finally their equal -- and backlit!
(Still which they were a tad cheaper, had bundles like the tradepaperbacks, and larger collections!)