I think Crafty may have meant Olfa cutting mat. I swear by the Olfa myself. Wait until you can get a 50% off coupon at JoAnnes or Hobby Lobby and get it then. I have the 24 x 36 size and when I checked walmart on line, I did not see them offering that size.
I did have a fiskars one but it didn't seem to last as long and some of the other brands seem to dull the rotary blades prematurely. so I stick with Olfa which has never caused me problems, other than the horrible smell when they are brand new. That goes away after a few days/weeks.