Some fans will cry out this trope whenever characters voiced by Steve Blum and Wendee Lee (perhaps most well-known for the voices of Spike Spiegel and Faye Valentine in Cowboy Bebop) end up in a romantic situation, even if one is a minor character that shows up for a few minutes in a single episode. Examples include the aforementioned relationship, as well as Samurai Champloo (where one of the pair really was in just a few minutes of a single episode), The Big O, Great Teacher Onizuka (though Lee voices half of the female cast and Blum has the lead role so it was inevitable), and even a Western animated example, Megas XLR.
Michelle Ruff usually voices a cocky strong willed girl with Liam O Brien as a character obsessing over her. First, in Gankutsuou, Ruff voiced Eugenie who spoke her mind without question, and O'Brien played Andrea, a guy who wants to marry her presumably just so he could get his hands on at least a part of her family fortune, and keeps following her around and flirting with her. Then in Odin Sphere, Ruff played Badass PrincessVelvet who goes around killing bad guys with her chain weapon, while O'Brien played her overly protective twin brother Ingway.
Then in Tales of Vesperia, Ruff played headstrong CuteGenius Bruiser Rita, one of the heroes of the game, and O'Brien played Cumore, one of the minor villians. Cumore didn't have the hots for Rita in any way, but they still were enemies.
There's also Persona 3 whereas O'Brien plays Akihiko Sanada, who's a good guy and while a Chick Magnet, the chicks he magnetized didn't include Ruff's Yukari Takeba, and for the whole part, they're good friends. They did come to blows in The Answer, when Yukari wants the Key of Time to go back to the past while Akihiko is against it, but it wasn't because of those lusting reasons above.
This may be more of a coincidence than any other examples here, but John Burgmeier and Chuck Huber made their start as playing two unlikely friends of different temperament on YuYu Hakusho, and while they really haven't been playing any definitively major roles together since then, they still continue to end up playing two very different characters that end up unlikely friends (or at the very least, acquaintances) on several works they've been in.
In fact, their son Nicholas was conceived during the dubbing of Dead Leaves, which is especially funny since Amanda's character becomes pregnant and gives birth during the story.
Also if a series was dubbed by ADV in the early nineties and featured three women, chances are very high that they'll be played by Amanda, Tiffany Grant, and Kimberly Yates. Examples include, but are probably not limited to, Gunsmith Cats, Burn Up!, and Devil Hunter Yohko.
And although this is pretty new, Puella Magi Madoka Magica isn't the first time Valenzuela worked with Carrie Keranen (Mami). They've worked together in the dub of Tekken: Blood Vengeance (Valenzuela as Alisa, Keranen as Xiaoyu). Then when Fate/Zero came, they were Sakura Matou and Maiya Hisau with Cristina as Sakura and Carrie as Maiya. It is later revealed that Carrie has been around working on League of Legends as Lux but kept it hidden until 2014, while Cristina's involvement as Riven (who came later after Lux) has been an open information since her debut.
Outside's Valenzuela's 'group', Lauren Landa has been involved a lot with Kate Higgins, usually as friends or allies. Their first 'grouping' can be said to be rather rocky, being Litchi Faye-Ling and Saya/Imperator Librarius, considering that Litchi was pretty much Forced Into Evil and not very happy about their alliance and Higgins was only doing Saya starting from Continuum Shift Extend. But afterwards, their 'relations' just kept getting friendlier, such as Yan Leixia and Natsu, Kasumi and Tina Armstrong (considering that they usually held no enmity to each other, and can be friendly per the Xtreme subseries), and Landa reprises Kasumi in Ninja Gaiden 3: Razor's Edge, in which she bumps into Higgins again, who's been doing Momiji ever since 2 Sigma (they don't meet in story, but since multiplayer co-op is available...). The only 'chink' so far is in Tales of Graces f, between Little Queen and Pascal.
Later in a further, Tales series, Tales of Xillia, Landa plays Leia and Higgins plays Agria, and the two are definitely not on friendly terms, repeating some of the chinks above.
Speaking of that, Lauren Landa herself has been also appearing with certain male actors together as of late (though relationship of the characters might not be so close together), with:
Twicenow, Johnny has played the more cerebral, black-haired friend of an excitable mecha pilot played by Yuri Lowenthal (Lelouch to Suzaku, Rossiu to Simon). Time will only tell if this trend continues.
As a contrast, more often than not, if there is one person who will/can kill Johnny (Lelouch, PJ, Firion played by CPU or friend, random ninjas), it's Yuri (respectively Suzaku, Pixy, Cecil if played by you, Sasuke). Doesn't work when the reverse is attempted (TTGL, Code Geass, Naruto).
To add to this, in TTGL and Code Geass, another character (played by Johnny and Yuri in those respective animes) usually ends up taking over the work the main character (Yuri and Johnny in those respective animes) has left behind - Rossiu took over when Simon left in Gurren Lagann and Suzaku stepped up to the plate after Lelouch died in Code Geass.
In the English dub of Mai-HiME, Mai and Mikoto's voice actresses play characters roughly similar to those they played in the dub of Strawberry Marshmallow. Carol-Anne Day (Mai) was Cool Big Sis-type Nobue Ito, and Caitlynne Medrek (Mikoto) co-starred as hyperactive and very-often mischievous Miu Matsuoka.
For that matter, Melissa Davis and Chris Patton are becoming this, as well, most notably being close friends in Kanon (Mai and Yuichi) and Demon King Daimao (Kena and Akuto), and against each other in Samurai Girls (Gisen and Muneakira) and ICE (Kisaragi and Julia).
Speaking of Yuri, he's had two roles playing a character hopelessly in love with a character by Kari Wahlgren, who only appears to have no interest on the outside. Those being Scrapped Princess and Durarara!!.
In Fullmetal Alchemist, they are rivals as Mustang (Travis) and Lust (Laura). Always one with a wicked sense of humor, Laura posted a pic of Lust getting burnt to a crisp by Mustang on her Facebook page as cover image on the eve of their first anniversary.
Kirk Thornton and Laura Bailey have voiced video game characters together. Particularly, they appeared in two Silent Hill games. In Shattered Memories, they play the voices of Harry Mason and his ex-wife Dahlia. Recently, in 3, Kirk plays Douglas, a private detective hired by Claudia, played by Laura, to find Heather. In Catherine, Laura is the titular character while Kirk is her boss, Thomas Mutton.
As for Barbie film fans, Kelly Sheridan would often appears as the titular character's (or rather, the role she play as), friend played by Maryke Hendrikse. They appear in The Diamond Castle as Liana and Melody, and in A Mermaid Tale as Merliah and Hadley.
In Wild Grinders, Fitzgerald plays Stubford and Lowenthal plays Goggles, one of the Wild Grinders who comes into conflict with the former.
There's also Catherine where Fitzgerald played waitress Erica while Lowenthal played Toby, an older woman lover falling for her. For the most part, Erica is mostly kind to Toby and that they're just good friends. In Katherine True Ending, Toby gets upset when he found out Erica is not really a girl, but has no problem of her hugging onto him.
And later on in BlazBlue: Chrono Phantasma, Fitzgerald plays the tomboyish hotheaded Bullet, while Lowenthal plays the flamboyant laid back gay Amane Nishiki. While not much focused, it is implied that they share some 'friendship' or sorts.