I've got loads of examples of bands that I tried to like a million times +1, but never actually got around to liking (prominent examples would be Radiohead, Tool, Opeth).
When it comes to music that I did eventually start to appreciate, I can't think of any single artist. There's loads of artists I kind of had to chew on for a little while before I knew that I really liked them, but it doesn't usually take a long time.
I'm either easily persuaded or not at all