#7 Kei Tomiyama
One of the classic anime voices of the 70s and 80s, Kei Tomiyama's tragically short life was nevertheless fruitful in his industry. Already well-known by the seventies for his role as the wrestler eponymous Tiger Mask, an character who has endured as an anime icon for decades, he went on to play a few other very notable roles. His tender, sincere voice at times belied his often firey delivery.
Something a bit less controversial:
#6: Masako Nozawa
It's hard to imagine a voice talent who delivers with more warmth, charm, and sincerity than Masako Nozawa. Though she's basically well-known only for a single character (and his look-alikes), it's that one iconic role and equally iconic performance that makes her worthy of highlight. That role, for those of you in a cave for the past twenty four years, is Son Goku from Dragon Ball/Z/GT.
#5: Ryo Horikawa
A voice actor with a lot of presence, Ryo Horikawa (born Mokoto Horikawa) had a strong presence in the 80s and 90s in Japanese animation. He's probably best known as the wicked prince of all Saiyans, Vegeta, in Dragon Ball Z, but he was acting before and has been doing work since.
#4: Yasuo Yamada
It may seem silly to highlight a voice talent who's known for playing one particular role, but when this particular VA's performance in the role is so iconic, and has spanned decades in that role, it's perfectly appropriate to me. Especially when the character he's known for playing is a favorite anime character: Arsène Lupin III!