Depends of what kind of BL you want... Can you elaborate?
If you like dark, psychological stories like Shintan Kairou,the one manga you need to read is Hagio Moto's Zankoku na Kami ga Shihai Suru.
As for artists who did BL, I really, really like Harada, basso (Natsume Ono), est em and Nakamura Asumiko. You can't go wrong with their stuff. I also liked Serizawa Tomo and Arai Niboshiko (Noda Ayako)'s styles. I recently discovered another BL artist who has a very cute style, Matsuo Marta... Tamekou is cute too. Speaking of cute, Itoshi no Nekokke by Haruko Kumota is one of the fluffiest BL. If you want to see some real drama, I recommend Sakura Gari by Watase Yuu, or Nemureru Mori no Binan and Tomoi by Akisato Wakuni.
And I'm not even a regular BL reader
Someone who's more into the genre can come up with much betters recs.