All of them.
Seriously. My company's policy is: if you're sick, call in sick. There's no set number of days...no "I've got a 103 degree fever and explosive diarhhea...but I'm going in, because it's July and I've only got 2 sick days left for the rest of the year." You're sick, you call in sick and stay home.
Of course, that kind of treatment also prompts a lot of "I'm too sick to come in...so I'll work from home today" kind of dedication from employees, so no one takes all THAT many sick days. And so far, everyone the company's hired (it's a small company, but grown from 5 to 50 people since I joined) has been honest about sick days, which helps as well. Still...it's a bloody generous system, particularly when accompanied by 20 vacation days a year above and beyond that for starting employees, and the 5% annual raise.
And before anyone asks...no, I'm not accepting anyone's resumes.