This is one of those little, niggling language things that has absolutely no impact on society, but still really drives me crazy when I see it in emails and on web sites because I am such a douche. One of these days, it will drive me to purchase an AK-47 and tour the country with a green bar report listing all the offenders, delivering swift justice Jay-and-Silent-Bob-style.

insure |inˈ sh oŏr|
verb [ trans. ]
arrange for compensation in the event of damage to or loss of (property), or injury to or the death of (someone), in exchange for regular advance payments to a company or government agency.

ensure |enˈ sh oŏr|
verb [ trans. ]
make certain that (something) shall occur or be the case.