I actually wrote a Hub about this, but here are some of my biggest annoyances:
* its/it's: Someone (mis)corrected me when I used _its_ as the possessive of _it_. I think this mistake occurs because we're used to seeing the apostrophe S used to show possession, such as "Julie's dog."
* stationery/stationary: I see this on pretty much any site that offers digital or paper stationery. More egregiously, I see it often on teacher sites. A guard at Buckingham Palace is stationary (unmoving). Paper and envelopes are stationery.
* comprised of: NO, NO, NO! The whole comprises the parts. The parts comprise the whole. The U.S. Senate comprises 100 members, but 435 members compose the House of Representatives.
* imply/infer: The speaker implies. The listener infers.
* farther/further: "Farther" is always used for physical distance. "Further" means "to a greater extent."
* The misuse of "literally": "I'm so hungry, I could literally eat a horse." " Literally" has to do with what is explicitly stated, such as a literal (word-for-word) translation.
* no/know: This one actually shocks me, but I do see it more than I'd like.
* "between you and I" or "for my friend and myself": "I" is a nominative program (meant to be used as a subject or predicate nominative). It is not properly used as the object of a preposition. "Myself" is a reflexive pronoun. It would be correct to say, for example, "I bought myself a book," because it shows action that you're doing for yourself. It would be incorrect, however, to say, "The waiter brought the food to my friend and myself." The waiter is not doing something for himself, and you are not doing something for yourself.
I have a special dislike for run-on sentences and sentence fragments, courtesy of Dr. Chapman and Mrs. Rossetti, my English teachers.