Split infinitives. Classic grammarians insist that we shouldn't put adverbs between the "to" and the verb form. "To actually think" or "to necessarily respond" etc. This is an example of a sin that has crossed over into questionable virtue: Even talented and informed users now employ this construction with impunity. But I advocate respecting the rule. If it's comfortable not to split an infinitive, I try not to.
"One of the ones." One of those.
"Kind'a" "Could'a" "I could'a been a contender." Kind of. Could have.
"Eck cetera." It's et cetera, stupid!
"Ex-presso" It's an Italian word, caffe espresso; there's nothing "express" about it.
"I axed you" This one makes my teeth ache.
"...which I did that." This bad grammatical error has crept into conversations throughout the media. Even college-educated moderators will attach this pronoun to begin a dependent clause in a sentence, then will proceed as if the pronoun were a conjunction. "A-Rod has said he didn't use the stuff after 2003, which the league has said it believes his decision." What results is two predicate objects in the same clause. "Which" should receive the action of the verb in any phrase it precedes. This is a stubborn misuse, which we'll have to be vigilant to stamp out. I don't see any excuse for it.
"Had I of had it, I wouldn't have had to get one." "If I had of done it...." Had of isn't English. Most educated people don't make this mistake, but it's almost an accepted form among the common legumes.
"He has got to be nuts!" This is a lazy use of the verb to get. The proper usage would be "he must be nuts!" To get doesn't mean to prefer; nor as an imprecation. Its proper use is to obtain, to acquire or to arrive at. "I gotta go" or "I've got to get going." You need to go!