I was going to list some of the more popular artists, but then figured this would be more useful:
Well if you want the full range, you should have a look at the oricon charts
. That has videos you can check out as well. In addition you have, I'm not sure I should call it sub-genres, but there's also stuff like Visual Kei which is aimed at certain groups of people. Anime fans are also a separate group in that respect, and in addition to anime and game soundtracks, they're usually fans of idol groups like AKB48 and Idoling. It's just important to realize that jpop isn't one genre, but instead a common name for pop music sold in Japan. Some of it has a more unique sound to it, but you can say that for some popular western bands as well.
Western fans of jpop tend to get rather skewed in their tastes as well, because we get exposed to a very limited selection of music. I think the one artist that has the number one appeal to pretty much most groups, is Ayumi Hamasaki though. She's the number selling jpop artist of all time, and even though her popularity's gone down a bit in later years, she's still managing to stay up there. It's not just the music though, but her stage presence - her live performances can be amazing. Even if you don't enjoy her original tracks that much, there's official remixes that IMO sometimes are much better.