I need to "freshen up" existing ceramic tiles in a kitchen. Are there any flooring materials that can be laid over the ceramic tiles?

Here are a few comments that others have made about materials being placed over ceramic tile. I can't attest to the accuracy.
As long as adhesions issues are resolved or expansion with laminates etc are considered, the other factor if using a heavy flooring might be the thickness of the sub-floor.
Tiling over ceramic tile - Remodeling Forum - GardenWeb (http://ths.gardenweb.com/forums/load/remodel/msg1214021813728.html)