umm, for melodic death metal that haven't already been mentioned...
Dark Tranquility - i honestly dont listen to these guys very often but when i do i am not dissappointed. kind of a strange growling vocal, but good instrumentation and atmosphere.
InFlames- yeah, dont get their newest three(?) albums, much more numetal/core ish, but their earlier stuff is pretty good, with some really great harmonized riffing and leads. lyrics and vocals arent bad either.
All that Remains - very good slightly on the metalcore side, but very talented, with a wide range of vocals and some epic riffery. apparrently they are also great live, which oddly helps me listen to them. something annoying about listening to a song then imagining a live version sucking.
hell yes on amon amarth.
you should try some thrash bands out as well if you havent already. a lot of people dismiss the genre as being just "metallica and slayer" but the lesser known ones are truly amazing. such as Testament, Kreator, Municipal Waste.