If you liked Arch Enemy, I suggest you check out some of the other melodic death metal bands in the Gothenburg style. Dark Tranquility would my first pick, Soilwork is pretty good too.
If we're doing band recommendations along AE lines, I'd throw in Barren Earth, Amorphis and Omnium Gatherum and Insomnium as well.
ne obliviscaris and wolves in the throne room are 2 other fantastic atmospheric black metal bands.
Soilwork - Stabbing The Drama is one of my favourite albums of all time.
In Flames, At the Gates.
I'd recommend old In Flames. Not the mostly-"nu"-metal stuff they've been putting out since Reroute to Remain. EDIT: And the new stuff is fine, but it's definitely not the fantastic melodic/progressive death they helped pioneer.