What are some good mystery mangas?

I've just finished Death Note and loved it, and I've started to get a bit of a taste for the mystery genre. However, I can't seem to find many really decent mystery mangas; I'd prefer one that is reasonably popular, is completed or at least has regularly published chapters (I've read several little-known mangas which are very good but the mangakas take ages to publicar chapters), with good characters and plotline-if it has a few psychological elements, all the better, though it doesn't matter so much. I'd be really grateful for any recommendations. :)