The melodies that have stuck with me the longest have been from Fugazi and Frank Black/Pixies. I think Frank Black particularly has a special sensibility when it comes to melody that often feels both novel and unexpected but simultaneously comes off really natural and effortless.
Damn no one has thoughts? I guess this is kind of a tricky question... I'm a poppunker, so I'll say that The Wonder Years really know how to write a melody that sticks with you.
In terms of extra-musical appeal, Kumi Tanioka is my favourite composer. I've read her described as a "storyteller", and yeah, I feel the places, people and events radiating from her music. It's dreamlike. Sky's The Limit is the easiest of her solo albums to find, but I really like the track Gustaberg that she did for Final Fantasy XI too.