 If you liked Shonan Junai Gumi! |  ...then you might like Crows |
Shonan Junai Gumi and Crows have quite a lot of similarities. Both deal with delinquents and gangs being formed in high school. There is strong focus on character development in both series and former foes becoming friends is recurring theme as well. If you liked either of them I think you would like the other as well.