Answer: Agree there's nothing worse, and let's face it... french polishing is not exactly cheap! But so often you end up covering beautiful wood surfaces, just to make sure the dreaded rings from mugs or glasses don't appear, and I know from experience, coasters only work if they are used!
Glass is one answer, but again, a piece of cut glass to the table shape is expensive, and there's always the risk that the glass can be shattered, so why not try clear PVC. The glass clear PVC looks just like glass, so you can still see the surface underneath, but is flexible, easily cut to shape with a sharp craft knife, long lasting and wipes down easily. It's also non slip, so less risk of items slipping or sliding anyway.
The PVC is food grade, cadmium free, heat resistant up to 60 degrees, and a relatively inexpensive way to protect a wide range of surfaces. The clear PVC is also great for the dining table either directly on the surface or to protect your tablecloth, I have one of those beautiful white embroidered tablecloths for special occasions which rarely see's the light of day, as it always ends up with something spilt on it, and is a nightmare to wash and iron! I've also used it on my bedside tables.
Available in 30cm, 100cm and 120cm widths, 'By the Metre' -click on this link to take you to the category.