I've never been a huge fan of play mats- you know, the ones you see used in pre-schools and play rooms all the time, and they generally just look tacky. These fantastic rugs have made me change my mind though! From Danish by Design, they are really cool. What little girl wouldn't adore the doll's house rug and the road rug is the best I've ever seen.
The rule to remember though is - don't use them decoration! Roll them up and put them away when the kids are finished playing and you don't run the risk of your house looking like the local kindy. (Although I could almost be convinced that the road rug could fit in with a "car" themed bedroom...)