Originally produced in Germany, and based on the Slackware distribution, they're now targeting North American users quite actively. S.u.S.E. uses their own "YaST" installation tool, and RedHat's RPM package management system.
They are now owned by Novell , and are certainly one of the big names for commercially supported Linux distributions. At work, we picked SuSE over Red Hat for our Opteron-based database servers due to getting enormously better service from the former...