Jason Marsden is the voice of Jack. He’s done a pretty good deal of work (both voice work and live, including a cameo in one of my all-time favorites--The Adventures of Brisco County, Jr.), and right now he can be heard as Virgil Hawkin/Static’s sidekick & best friend Richie Foley on Static Shock and as Snapper Carr on Justice League. Here's a picture of Mr. Marsden I found on eBay.
Rene Auberjonois is the voice of Xyber 9. He's probably best known for his role as Odo on Star Trek: Deep Space Nine. He's done a ton of VA work, as well, having done work recently for (what I think is) a remaster of The Last Unicorn, Ganthet on Justice League, and roles in the Legacy of Kain game series. If there's any other work of note that hasn't come to my attention, please let me know.
Nika Futterman is the voice of Anakonda. Credits I’ve found for her are largely guest shots on series such as Time Squad and what looks like a regular role on Hey Arnold! She's also done the voice of Mike on Mike, Lu, and Og for Cartoon Network. I've seen her billed for these roles under the name Nika Frost as well, so maybe I'm just looking in the wrong places. Any other credits would be greatly appreciated. THIS JUST IN!!! Apparently, Ms. Futterman also did some vocal work in the Offspring's immortal ode, "Pretty Fly for a White Guy." You don't know how much I respect her for that.
Quinton Flynn is the voice of Mick. My favorite voice actor, he has most recently earned the hatred of every overgrown 12-year-old guy who played Metal Gear Solid 2 by voicing Raiden. He has also done Johnny Storm/the Human Torch on Fantastic Four and Jonny Quest on the second season of The Real Adventures of Jonny Quest, as well as tons of guest vocals on shows including Samurai Jack, The Mummy, Spiderman (a Secret Wars story), and several Cartoon Cartoons. He also sings in a band called the Snozzberries at festivals & such. Here's a nice collage picture of Mr. Flynn made by Ina-chan after he guested on Leap of Faith.
Rodney Saulsberry is the voice of Willy. He has done lots of work, including announcer credits on lots of movie trailers. Superhero animation fans will recognize him as the voice of Robbie Robertson from Spiderman. Other than that, though, I can’t find a lot for him; any more credits would be appreciated.
Tony Jay is the voice of Machestro. This guy’s done just about every villain ever, thanks to his Darth Vader-like voice. He’s probably best known as Megabyte on ReBoot.
Tim Curry is the voice of King Renard. I truly pity those that have not heard of this man; he is as close to GOD as you get with this cast (although Quinton Flynn has a special exemption). He will forever be known, much to his chagrin in all likelihood, as Dr. Frankenfurter in Rocky Horror Picture Show, and he’s done the voice of King Chicken on Duckman and played the Head Wizard in an acid trip of a movie called The Worst Witch.
Jolie Jenkins is the voice of Princess Rozalyn. Her stuff is mostly live action. She had a regular role in a show called Shasta McNasty, which I have never heard of before in my life. She has also guested on X-Files, The West Wing, and Party of Five. Lessee... one show I respect but don’t necessarily like, one show I’ve never heard of, and two I don’t like... Nope. Still hold my negative opinion of her performance.
Two of the mystery VAs frequently billed as having involvement with Xyber 9 are Phil Buckman and Christopher Marquette. Mr. Buckman had a role on a drama called City of Angels; I believe it was about a hospital, but it wasn't something I watched regularly. I'll bet dollars to donuts he voiced Slick in "The Golden Masquerade", but there's no definitive credit for this. Mr. Marquette can currently be heard as the voice of Alex O'Connell on The Mummy Animated Series (although if you're anything like me, you're suspicious about animated shows based off of movies and hence, haven't seen it). I'd love to know who, exactly, Mr. Buckman and Mr. Marquette voiced on the show to give them a proper credit.
Unfortunately, I have been unable to find out who provided the voices of Ikira and Queen Tatania. If anyone knows, please let me know and please do the same if you know of any credits for any of the other VAs or who any of the incidental VAs might have been. I’ll be sure to give you credit.