Hudson_Hawk:Once you get your grout clean, be sure to seal it. Most people don't realize this is something that should be done every so often. It helps keep mold, mildew and dirt from staining your grout. I've also heard good things about ZEP grout cleaner...
Ditto this. My MIL (the queen of clean) deep cleans her grout twice a year and reseals after the cleaning. It always looks great!