My attention was just drawn to one: "mop cap" for "mob cap".
Without a doubt, "mob cap" is historically and etymologically correct, and the vastly predominant form in print. See Google Books Ngram Viewer for a frequency comparison ("mob cap" vs "mop cap"). The etymology is a murky one. It's not from "mob" as in crowd (a contraction of mobile vulgas = fickle masses), but, according to the Oxford English Dictionary, from a 17th century word "mob" (= "A wench, a slattern; a promiscuous woman; a prostitute"), with possible interaction with the 17th century "mobble" or "moble" (= "To muffle (a person, or the head, face, etc"). This acquired further connotations of informality of female dress - a mob or mod-dress was "A loose informal garment for a woman" - until by the late 1700s we had:
A large cap or bonnet covering much of the hair, typically of light cotton with a frilled edge, and sometimes tied under the chin with ribbon, worn indoors by women in the 18th and early 19th centuries.
The term had shed its disreputable origins, and the imitation of rustic clothing had become chic; the mob cap, often in very florid forms, was worn by highly respectable ladies. Here are some images of wearers from Wikipedia: Elizabeth Sewall Salisbury (1789), Marie Antoinette (1792), and Mrs Richard Yates (1793).
By the end of the 19th century, however, it had ceased to be fashionable, and only maids, servants and menials were wearing mob caps as utilitarian headwear. I'm sure this is how the eggcorn originated; the mistaken idea that it was a cap worn while mopping things.
The eggcorn is not unknown even historically, as in this 1835 example:
Barl. I ax pardon. Miss, will you be kind enough to go boil the lobsters for the company? Dang my buttons, this is letting you go to Blandford races. I'll buy riding habits and feathered hats for you—go put on your mop-cap and white apron—there's the keys— get along.
- The London Hermit, John O'Keefe, Alexander's Modern Acting Drama, 1835
... and in a handful of other examples from the second half of the 19th century.
But by far the most appearances are in the past decade. At least in books since 2000, "mob cap" still predominates - "mob cap": 2630 hits / "mop cap" 146 hits - though with the surprising occasional appearance in scholarly books by people who ought to know better (for instance, page 255 in Helen Bradley Foster's New Raiments of Self: African American clothing in the antebellum South). But on the Web in general, the eggcorn has come to account for around a third of all occurrences of the term - "mob cap" 429,000 hits / "mop cap" 224,000 hits. - where "mop cap" is mostly being propagated by costume hire and fancy dress websites.
It's enough to turn you prescriptivist...