In A Different Lesson, the Wu Sisters start out as this of Ozai'sAngels, with Xiu standing in for Azula, Chun as Mai, and Jia as Ty Lee. They aren't exact copies, but the author does have a fair amount of fun with this, and they drop a lot of familiar lines. They also end up growing and developing as characters in their own right.
The Ranma ˝Elsewhere FicBoy Scouts ˝ follows mostly a cast of original characters, although some of them are obvious expies of characters from the original work.
The Porter sisters are expies of the Tendo Sisters, with Sarah being the tsundere love interest of the main character (like Akane), Kirstin being the cooking and cleaning caregiver (like Kasumi), and finally Nicole being the money lover with questionable principles (like Nabiki). This is lampshaded with the first names of Kirstin and Nicole starting with the same letters as those they are expies of.
Despite being based on a real person, as a large chunk of the Boy Scouts ˝ cast is, the character of Derek Provost is also an expy of Happosai.
Taylor Kuntz shares his initials with Kuno Tatewaki and is basically what you would get if you took away Kuno's pretension of class.
And oddly, in a case not based on Ranma ˝, the character of Justy Yung is an expy of Jinnai Katsuhiko from El-Hazard. This was even lampshaded in Universe when some of the other characters were watching that show and thought Jinnai seemed familiar.
In Children of Time, Kit Bennett, alias Kathy Watson, is clearly an expy of River Song. The parallels aren't in full, but dang if they don't go far, with everything about Kit in her introductory episode echoing many elements of River throughout her tenure on Doctor Who.
Most of the characters in My Little Unicorn are expies. Made most obvious in one of the author's YouTube videos explaining his characters, clearly showing that they are recolors of the original show's cast!
In My Brave Pony: Star Fleet Magic III, Raven, Twilight's assassin, is named and based off the Teen Titans character.
Reality Is Fluid: The author's note states that Professor Atani Dukat of the Cardassian Science Ministry was partially based on Emperor Turhan of the Centauri Republic from the Babylon 5 episode "The Coming of Shadows". Both are members of an enemy culture who are trying to atone for their peoples' past crimes by apologizing to representatives of those they harmed (Kanril Eleya, a Bajoran captain in Starfleet, in Dukat's case, Ambassador G'Kar of the Narn in Turhan's). The comparison is only partial, however, as Dukat's attempt turns out much better.