Custom Building Products Aqua Mix Sealer's Choice Gold 0.8 qt. Penetrating Sealer for Tile, Concrete, Porcelain, Stone and Grout AMSC24Z - The Home Depot
CoverTec GlazeGuard Satin Ceramic And Porcelain Tile And Grout Sealer, Satin Finish, (2 Part A+B=1 Gal Kit) - Amazon.com
Miracle Sealants 511 Spray-On 15-fl oz Clear Ceramic/Porcelain Tile Grout Sealer in the Indoor Floor Sealers department at Lowes.com