I made the diaper clutch based Gretchen F's 'How To'.
I had a fabric I wanted to use though so I didn't use place mats, instead I worked out the sizing for to cut it out of fabric (see PDF attachment for my pattern).
I also used a clear plastic vinyl outside the fabric to make it easy to clean (as babies tend to be messy!) and put a press stud closure.
As these were gifts for people I also made matching change mats to go inside the clutch. The ones I made are 55cm x 55cm with rounded corners (I used a glass to get the right shape), with 2 layers of fabric (my contrast fabric is poplin) and bias tape trim.
For the pink one I also did a matching bib! You can find the pattern for that at http://www.newconceptions.com/free.htm