Okay I'll just post my newly updated master list now:
Umbrella: Karen Strassmen. Last I checked she voiced Nanako who had that cute girl voice that I would think would fit Umbrella well enough.
Black Dahlia: Her:
Annie: Melissa Fahn. All I have to do is point to her work as Gaz from Invader Zim and that should justify my reasons.
Stanley: LittleKuriboh. Need I say more?
Hive: Cassandra Lee Morris. She certainly fits Hive's brash attitude well judging from her previous work.
Leduc: Him:
Or Lucian Dodge. Whoever of the two Lab Zero can get.
Illeum: Kari Wahlgren. She's already voiced a motherly headless horsewoman, why not a motherly cyborg intestinal tract thing?
Brain Drain: Crispin Freeman. If he can do Alucard, he can sure as hell voice a robot bodied brain in a jar w/ psychic powers.
Andy Anvil: Kirk Thorton. I just gotta point to my avatar as evidence that he can do a cartoony guy like Andy.
Tommy Ten-Tons: Charlie Adler. I present you with this evidence as to why:
(Seriously, am I the only one who sees a resemblence?)
Feng: Amanda Winn Lee. Maybe I'm just playing too much Persona lately but I do think she'd fit.
Taliesin: Sam Riegel. I've got nothing more to add then that.
Regina: Mary Elizabeth McGlynn. She sounds commanding enough.
Beatrix: Erica Mendez.
Ottomo: Tom Kenny. He should also voice Tom as well.
Irvin: Kaiji Tang. I just need to point to Voices of Gaming for that.
Yu-Wan: Patrick Seitz. Just take Simon from Durarara and have him replace the Russian accent with a Chinese one. There you go.
Minette: Hynden Walch. Do I need to go in-depth with that?
Panzerfaust: GeneralIvan. Enough said.
Adam: Kyle Hebert. Because he plays over the top characters too much these days. Let's see him voice someone humble for once.
Venus: Tara Platt. Going by work and how she sounds, she'd work.
Aeon: Bridget Hoffman. If Digimon Tamers and Gurren Lagann have taught me anything it's that she seems to be the one to go to for emotionless cosmic horrors.
I also have a few for characters that we only know about in conceptual form like that knight formerly named George in the digital art book or ones that have been dug up by web surfers like Silverwind and Fuscienne but I'll leave those off for now given there's no evidence that Alex will ever revisit those characters at the moment. (Hell Silverwind and Fuscienne only have names and small summaries. We don't even know what they look like!)