Will adding a french drain and sealing the wall be sufficient to waterproof a basement?
If the crack is visible from inside, you could use an expanding polyurethane foam kit. I've used one from RadonSeal in the past (http://www.radonseal.com/crack-injection/diy-injection.htm) and had great results. You can also inject the crack from outside if that's easier. I'd also check grading (is soil sloped away from the house?) and drainage (no close downspouts, etc) outside to make sure any easy water sources are taken care of.