Looking for website/software that does patio block pattern generation

My lovely bride and I have decided to tear out our brick front walkway and replace it with patio block. We are currently leaning towards a concrete patio block style that comes in either three or four different sizes.

I recall reading about a software program for stacking different size boxes on a shipping pallet; you enter in the number and sizes of the boxes and the software would generate a diagram of the most efficient stacking method.

Is there some website or software available for entering all the information (area of walkway, size and number of sizes of blocks, etc.) and have it generate a pattern or patterns that would fit?

Bonus points for being web-based or Mac software.