I'd like to see Sean Schemmel! We've already got Chris and Chuck, so why not throw in the main character of DBZ~?
Cynthia Cranz would also be great, and if we could somehow manage it, Scott Mcneil. Because I adore that man, but never got a chance to meet him.
For Japanese Voice actors, I would like to see Suwabe Junichi (Undertaker, Atobe Keigo, Yukiya, etc.) and Hikaru Midorikawa (Tamahome, Heero Yuy, etc.) I know Suwabe is still pretty active, but I'm not sure about Hikaru. Also Miyano Mamoru is always a good choice, he's in everything (Kida Maosami, Tamaki Suou, Kira/Light Yagami)
Also for a musical guest, I would love to see the band D (
http://d-gcr.com). They're a great bunch of guys, and always willing to come back to America and do a show (They really want to come back. They like it here lol.) They're a J-ROCK band, but they're awesome, and actually love anime and get all hyped up at cons. (I saw them at Akon. They were nuts!)
A lot of these bands that people are asking for are too popular (L'arc~en~Ciel, Gackt, Megumi Hayashibara), and so I don't think their contracts would allow them to come overseas. However, smaller bands that are more independant, like D, and Ayabie, maybe even Gazette if you can get the contract to allow them, would be a great band to see. Matenrou Opera is also a good choice, Kamijo is always good, anything in the independent labels.