1: Loose for lose

No: I always loose the product key.

Yes: I always lose the product key.
2: It's for its (or god forbid, its')

No: Download the HTA, along with it's readme file.

Yes: Download the HTA, along with its readme file.

No: The laptop is overheating and its making that funny noise again.

Yes: The laptop is overheating and it's making that funny noise again.
3: They're for their for there

No: The managers are in they're weekly planning meeting.

Yes: The managers are in their weekly planning meeting.

No: The techs have to check there cell phones at the door, and their not happy about it.

Yes: The techs have to check their cell phones at the door, and they're not happy about it.
4: i.e. for e.g.

No: Use an anti-spyware program (i.e., Ad-Aware).

Yes: Use an anti-spyware program (e.g., Ad-Aware).

Note: The term i.e. means "that is"; e.g. means "for example." And a comma follows both of them.
5: Effect for affect

No: The outage shouldn't effect any users during work hours.

Yes: The outage shouldn't affect any users during work hours.

Yes: The outage shouldn't have any effect on users.

Yes: We will effect several changes during the downtime.

Note: Impact is not a verb. Purists, at least, beg you to use affect instead:

No: The outage shouldn't impact any users during work hours.

Yes: The outage shouldn't affect any users during work hours.

Yes: The outage should have no impact on users during work hours.
6: You're for your

No: Remember to defrag you're machine on a regular basis.

Yes: Remember to defrag your machine on a regular basis.

No: Your right about the changes.

Yes: You're right about the changes.
7: Different than for different from

No: This setup is different than the one at the main office.

Yes: This setup is different from the one at the main office.

Yes: This setup is better than the one at the main office.
8 Lay for lie

No: I got dizzy and had to lay down.

Yes: I got dizzy and had to lie down.

Yes: Just lay those books over there.
9: Then for than

No: The accounting department had more problems then we did.

Yes: The accounting department had more problems than we did.

Note: Here's a sub-peeve. When a sentence construction begins with If, you don't need a then. Then is implicit, so it's superfluous and wordy:

No: If you can't get Windows to boot, then you'll need to call Ted.

Yes: If you can't get Windows to boot, you'll need to call Ted.
10: Could of, would of for could have, would have

No: I could of installed that app by mistake.

Yes: I could have installed that app by mistake.

No: I would of sent you a meeting notice, but you were out of town.

Yes: I would have sent you a meeting notice, but you were out of town.