Essentials of Music Theory
Learning Music Theory: Absolute Beginners: Section 2
There is no substitute for memorization and practice. I haven't found any other sites that drill note names so I decided to make my own.
The note name game will let you choose your clefs and drill
you as long as you want. Really, if you're not getting at least 49/50 if whatever clef you're trying to learn then you should keep practicing
until you get there. You'd be surprised, even at the graduate level, how poorly some music academics do in clefs outside of their own instruments.
Anyway, good luck with the note name game.