Voices! :D
I'm much more natively audio-oriented than Alicorn, so I can dig into this a lot faster from the get-go.
Broadly speaking, boy Tonies sound like Robert Downey Jr as Iron Man and boy Sherlocks sound like Robert Downey Jr as Sherlock Holmes - except that Sherries also carry an influence from Paul Bettany as Jarvis, where applicable. The girl versions have virtually the same cadence and intonation, with only very slightly higher pitch. In worlds where the local accents don't map onto Earth ones, I still imagine them having roughly the same respective voices where at all feasible; for example, Pearl's Capitol-influenced accent sounds a lot like an English accent in my head. From worlds where they can't feasibly have very different dialects - Iron and Steel in Chronicle, Tia and Sary in Quinn - I usually default to imagining them both as closer to the standard Tony Americanized accent, except that Sherlocks still carry their distinctive cadence and vocabulary. Special mention for Minus: Minus speaks in a way that is noticeably distinct from other Sherlocks in general. You mostly hear it in word choice, though, and just a little in intonation. Also, Sherlocks are phenomenal vocal mimics and can put on any accent they hear enough of.
Matildas sound like Mara Wilson in the Matilda movie, aged-up where applicable, which might not end up sounding like what Mara Wilson actually sounds like because I haven't heard enough of her grown-up voice to internalize it. There is one Matilda from England who has never spoken onscreen and she sounds like that, but in an English accent.
Ekador Serlast sounds exactly like Ichabod Crane in my head. This is probably not feasible given that he's not from an Earth, but I'm totally going to imagine him ending up with exactly that accent when he learns and begins speaking in English.
Now to go through all my templates in the spreadsheet, sorting for ones you've actually seen...
Bridget Banner sounds like a feminine version of Mark Ruffalo's Bruce Banner, with some influence from Amy Acker as seen in Angel. They mesh surprisingly well in my head.
John Blake sounds exactly like he does in canon, which I'm given to understand is pretty much just Joseph Gordon-Levitt's voice.
Chainsaw sounds a lot like David Boreanaz as Angelus on Buffy/Angel, with subtle differences I'm having trouble describing. His younger alts like Sandy and Dao don't have well-developed voices in my head, but can be assumed to mostly sound like a younger version of that, modulo the obvious fact that Dao has not yet actually spoken English and probably sounds way different speaking the native language of the AtLAverse.
Eights and Anna and their alts, surprisingly, don't have well-developed voices in my head either; they mostly just sound exactly like my internal monologue. From what I remember of Rebecca Hall as whoever she played in Iron Man 3, you probably won't go far wrong if you imagine that voice for Eightses.
Darcies sound exactly like Darcy Lewis in the Thor movies.
Dominiques don't have well-developed voices in my head; you may assume that Yseult sounds Vaguely French, Damaris sounds like whatever Samarians tend to sound like, and Helen's accent resembles Kas's. If you want to imagine them with Anne Hathaway's general timbre, be my guest.
Finches and Hilaries don't have strongly well-developed voices in my head, and you can largely assume that they sound like they belong in Forks, except when they appear in places other than Forks, where you can assume they sound like they belong there instead.
Ikes sound (I just looked up the movie trailer on Youtube to check)
exactly like Michael Cera as Scott Pilgrim. Vals probably don't sound anything like Emilie Dequenne, as I've never heard her speak. I would describe the voice of Vals in my head as louder and... steadier? than Ikes, but with basically the same accent and frequently similar intonation, adjusting for the fact that Vals have well upwards of double the self-confidence.
Jnis (Janine and Junia) probably don't sound like their facecast, because I've never heard her speak either. They have a broadly similar speaking style to Ikes, except that where Ikes are sort of a little bit breathless a lot of the time, Jnis instead tend to sound bright and cheerful. As for the baseline timbre of their voices, I'm not sure, but you can probably get somewhere by imagining a more feminine Ike.
Jokers... are complicated. By and large, they range from sounding like Heath Ledger as the Joker to sounding like Heath Ledger as the Joker minus the more exaggeratedly weird cadence and emphasis. If you're not seeing vowels italicized in the middles of words, default to imagining the latter. Female-PB versions sound largely the same, but a little more feminine. The difference is small, however. Miscellaneous other PBs also sound largely the same, although they may vary in details too subtle for me to capture. Other variations exist: Winter in particular is likely to have picked up the Vaguely English Narnian Accent; Micaiah has a noticeably wider vocal range for singing than Joker average, which he sometimes employs in regular speech; Beast is Vaguely French; Felicity is twelve.
Kolyas are Russian, but speak fluent English with very little accent. You probably wouldn't go far wrong imagining Aldis Hodge, although I think he might not usually sound like he could plausibly be from Toronto, which Kolya does. Lazaruses
are in fact from Toronto, except for the ones who are from non-Earths, but they all sound the same in my head. I don't actually know what Adrien Brody sounds like, so Lazaruses probably don't sound exactly like him. Oh, and then there's the demon Lazarus from Sunshine - heck if I know what he sounds like, but I'm reasonably likely to describe it if he ever speaks onscreen.
I do not know what Liselen sounds like. Well, I can hear him in my head, but I don't have a good reference for it. He defaults to the same accent as my internal monologue (and I am from Toronto), but I haven't firmly decided that that is actually how he talks.
I just looked up Drew Barrymore on Youtube to see if Chrises sound like her, and I found her talking to Ellen DeGeneres, and discovered that Chrises sound a lot more like Ellen DeGeneres. But Chrises are very rarely as excited as these people are getting. Go look up Drew Barrymore talking to Ellen DeGeneres, and imagine a merge of their voices with a more Ellen-like timbre and a more Drew-like accent, but very calm and dry and without that little uptick in intonation at the ends of sentences that Drew does a lot of and Ellen a little.
Jameses sound broadly like Chrises, but their voices might be a little higher. I've looked up Ellen Page, and I think she's a pretty good model for the timbre of young Jameses. Older Jameses (as portrayed by Sophia Bush) sound like that, but... older. XD They get even closer to Chris's deadpan intonation as they grow up.
Giles sounds exactly like he does in canon. His younger alts speak in a noticeably different English dialect, but I don't know enough about the available options to confidently choose one.
Ethan Rayne and his alts all sound pretty much exactly like he did in canon, with appropriate age and (for some you haven't seen) gender variance.
Nathaniel, Voice, and their alts are an interesting case! All of their voices are based in my head on the character of Steven from Alice Cooper's albums Welcome To My Nightmare and Along Came A Spider. Nathaniel sounds broadly like... well,
this, except less creepy. Voice sounds like roughly the same person speaking as described in Voice's narration, in that weird whisper. Nathaniel used to sound a lot closer to Voice when he was a child (except, again, less creepy), but now that he's grown up he's gotten less quiet, closer to the "no I'm a great big man"/"no Steven you have to go back now" in that video. Other alts may vary depending on individual circumstances; you might find it instructive to look up the Along Came A Spider album and listen to some of the speaking segments in those songs, to get a good idea of the range they vary over.
Thor's female alt sounds like Thor, but female. And minimally changed from the original Thor.
Pepper Potts and her alts sound exactly like Gwyneth Paltrow as Pepper.
Howlett sounds exactly like Hugh Jackman as Wolverine; Lycaelon sounds similar, but younger; Luhan is pretty much exactly like Howlett.
I mostly don't have a firm idea of what the dialects from the various non-Earth worlds sound like, except for things like Pearl's Capitol accent sounding Sherlock-English in my head.