My favorite VA would have to be J. Michael Tatum, because his role as Isaac in Baccano! was amazing, and because it was Isaac, it made it that much more awesome.
Kappei Yamaguchi (L, Ussop, and Ranma) is also one of my favorite seiyū. He played L perfectly, and was a pretty cool guy when I met him at Animazement 2010 (he signed the Death Note I bought in the Dealers Room, I felt really bad afterwards though)
"P.S. Go screw yourself, I haz da powerz!!!!!" -Chiaki "Fall off a cliff and then return in a month in an opera mask?"- Aroduc "The Hammer of Justice is unisex" - batman The world tastes like strawberries "My future's so bright, I can't even see it!" "cast in the name of god ye not guilty"
The first that comes to mind is one that I hate: Greg Ayres. I'm so disappointed when he is the main character and have many times just stopped watching the show. I don't mind so much if he is a massive nerd side character because his voice fits it.
The ones I like are pretty generic: Vic Mignogna (Ed Elric), Steve Blum (Spike), Chris Sabat (Vegeta), Wendee Lee (Faye), Johnny Yong Bosch (Ichigo and Vash), Travis Willingham (Ginko and Mustang)
They're all dub actors because I can't really tell a good Japanese voice actor from a bad one.
Japanese: Norio Wakamoto (Nobunaga in Sengoku Basara, Cell in DBZ, Emperor in Code Geass) - This man has such a fun and manly voice. Rolls his R's like no tomorrow, and it never grows old. He's done a ridiculous amount of voice work.
Megumi hayashibara (Lina in Slayers, Rei in Evangelion) I can't get enough of her, mostly for her sole as Lina in Slayers. She's also a great singer.
Cam Clarke (Liquid Snake in Metal Gear Solid, Kratos from Tales of Symphonia) If anybody's voice could turn me gay, it would be his.
Luci Christian (Tenma Tsukamato in School Rumble, Iwasa Irie in Angel Beats Kanae Chidori in Fullmetal Panic) She's got the perfect voice for an excitable energetic teenage girl. She fit Tenma absolutely perfectly, and she's one of the main reasons I prefer that show in dub.
Shelly Calene-Black ( Cleao in Orphen, Canaan in CANAAN) Great voice actress for an adult woman's voice. I wish she had more roles.