Freshen up your tile grout with this product from Home Depot for under $15.  Your grout will look clean and new and you can even change the color of your grout.  I paint (or hire my daughter.....read on) my kitchen grout every couple of years.  I used a carpet-cleaning company once, but my 13-year-old does a neater job at a quarter of the price!  It's a great project for a teenager to earn money and be helpful around the house.  Use a foam, angle-tipped brush and be sure to test the color first - there are many to choose from.