I see college students making the same mistakes over and over, so I have to speak up.

Than/then: Then is used for sequential events. Than is used for options.
"I did the lab assignment, then the homework, then took the quiz."
"Other than that, Mrs. Lincoln, how did you enjoy the play?"
"I'd rather go to the mall than go to school."

Affect/effect: Affect is the verb, effect is usually a noun. A flat tire will affect the handling of your car, or will have an effect on the handling of your car. Effect can also be a verb, meaning to cause or create, as in, "Some people, in order to effect a change in Washington, voted for Obama, but so far it has had no effect."

Their. I'm an English purist, and even though "their" has been used as a singular pronoun of indeterminate sex for almost 500 years, it still sounds wrong to me. I don't like it, and I correct it when I see it.

The use of apostrophes in plurals. This one just plain drives me up a tree in short order. Apostrophes denote missing letters or show possession, NOT plurals.

Calling * an asterik. There's another s in there. It's asteriSk.

Aks, as in "Can I aks you a question?" (I always reply, "you just did"). An axe is used to cut trees. You ask permission to cut the tree down.

Ect. When did our English teachers become so ignorant that they can't teach students that etc. stands for "et cetera" (and so on) in Latin. Who started this "ect" thing? He/she needs to be hauled out and shot in the pencil case.

Complimentary/Complementary: Complimentary means free. ComplEmentary means two things that accent each other, such as "A knife and a fork are complementary utensils."

Stationery/Stationary: I saw an "educated" person misuse this one. A stationery store is where you buy stationery, also known sometimes as a stationer. The store itself, since it does not move, is stationary.

The -able/-ible suffixes. The rule I remember from grade school is that if it's a verb involving action or motion, its "-able", as in "movable" or "drivable". If it does not directly connote motion, then it's "-ible", as in "collectible" or "legible".

"seperate". Always remember there is "a rat" in the middle of "separate", whether a verb or an adjective.

elementary/alimentary: Alimentary deals with eating and digestion. Everything else is probably elementary.

Me vs. I. One of my former students threw up pictures on Facebook entitled "Ericka and I". This is wrong. Would you say "I" or "Me"? Now put Ericka back in the picture and the answer is the same. "Ericka and me". Ericka and I would be propoer if they were the subject of a sentence, but the implied sentence on the photo caption is "[There are photos of ] Ericka and me."