Two kills that fit the Code that Dexter generally regrets:
>Miguel Prado
>Brian Moser

These don't fit the Code and Dexter generally killed someone innocent

>Rankin (just an asshole)
>Clint McKay (to save Hannah McKay)
>Jonathan Farrow (confirmed innocent man who was ritually killed)
>Logan (to save himself from getting caught)

Regrets Farrow and maybe Rankin

-----
>Nathan Marten (p*do targeting Astor)