I have a Dritz cutting mat and I honestly haven't had any problems with it.

My favorite is the omnigrid. I find it is a little firmer than the Ofla, but not as hard as the June Tailor. I also use one that I bought in the scrapbooking section, it is a gray Martha Stewart board.
I also find the Ofla mats stink way too much for my nostrils.

I have a pink Olfa one 18"x24". It was a limited edition for Breast cancer a couple of years ago. There are still a few around, but pricey.

I have an Olfa and it has not been worth the money. I never thought I was very stong and I know my blades need changing but have had to duck tape where it has cut through. And yes, I have tried to cut in different places. I am looking at an Alvin..self-healing, 3mm thick (supposed to be thicker than an olfa or Fiskars), and is used by graphics designers, framers, sewing, etc. So I assume since it is used by the "professional" people, it would be a stronger mat than the others mentined. The price is about the same. Anyone used one of these?

I second the recommendation about avoiding those white mats at Joann Fabrics. I used to replace my blades way too often when I had the mat from Joann's. Then I bought the "big mat" from a quilt show vendor as a show special. They come in several sizes...here's the link. sewingemporium.com I noticed how blades don't need to be replaced as often...even the ones I sharpened on the electric rotary blade sharpener by True Sharp. There is even a warranty, which I have not seen before.

I just ordered an Alvin 42x30 from Amazon yesterday for $50. I've been needing a bigger mat and have been researching what best fit all my needs and that's the one that I ended up with. I'm a notorious researcher in my family, they all pick on me and make jokes(it takes me a week to buy a loaf of bread because I have to check reviews from at least 7 different sites first), but the thought of buying something on a whim makes me ill.

A big factor for me was the thickness of the Alvin, as the Fiskars I have now isn't that old, less than a year, but is almost cut through in a couple places. I don't cut on the same lines over and over either, I always vary it. It should be here Tuesday, I'll try to remember to come back here and give a first day review, I hope it's a good one.

Ive been using a yellow for over four yrs. No problems.

I have a Martelli matt and love it. Have had it for 7 or 8 years and cut every day. There is no visible cutting marks and my blades last forever. I know they are pricey but have saved a ton on blades. One side is yellow and the other side is purple.

I just bought an Olfa at Joanne's. It was 50% off plus my teacher discount of another 15% off. It was a great deal!