I've had good luck with self leveling polyurethane. If the crack is deep I put some foam backer rod in first. It's gray but you can tell it's caulk if you're concerned about looks. It's really gooey and can be messy before it cures but if you're careful and put it where you want it the first time, it looks pretty good. I put some in cracks 5 years ago and it's still just as good as it was when I did it. I did all my expansion cuts with it too since Michigan gets a lot of thawing/freezing which opens cracks up fast. For small cracks I use a concrete blade in my skil saw to open the crack up a little and fill it to stop it before it gets big.
The stuff Croatoan found is good too. For me the polyurethane is easier and indestructible after it's cured. If it wasn't dark and raining I'd post a pic.