The "On Stage" album from Rainbow is chock full of great Dio performances, when he was more melodic and not so much growlie that he likes to do now. That's my favorite RJD era....when he was more of a singer. The only thing that could've made that album better would've been including Stargazer.
But, I'd have to say Kill The King (Rainbow), Die Young (Sabbath) and Don't Talk To Strangers (Dio).