These are my biggest two, but there are others:
- loose (not properly contained or improper fit) vs lose (lost or misplaced)
- insure (warrant against damage, i.e. get paid if it breaks) vs ensure (take action before an event, i.e. keep it from breaking in the first place)
Another thing that annoys me is the folks that tsk-tsk over crimes, but can't/won't take the time to get involved in stopping or preventing them. A couple of years ago, I was leaving the public library when I heard some guy yelling a block away. As I got closer, I could see that he was directing his ire at a young woman -- and more, that he was physically intimidating her (getting in her way when she wanted to leave, etc). I didn't witness any actual physical contact, but it sure sounded likely. When I got close enough to see what was going on, I set aside the other things I had to do in favor of keeping myself available in case the guy DID start any physical abuse; I also got a passer-by to call the situation in on their cell phone. The cops showed up, and it turned out that there were actually a couple of us ready to intercede if the guy had started anything -- out of the several dozens of people that simply stood around watching, and looking stupid. The other person and I both gave statements to the cops, and indicated that we were willing to testify in court if necessary. Nobody else could be bothered, or wanted to get involved. As far as I'm concerned, it's a lot like the political process: if you aren't ready and willing to be an active participant, you don't have any right to bitch about the results.