Hmmm...my suggestion is really low tech, but I used it for the 2008 growing season and it worked very well.
Graph paper (1/4-inch grid or 5 to the inch) and pencil. Get a GOOD, large eraser.
Measure your plots. One sheet of graph paper per plot. Write down each plot's scale on its particular sheet of graph paper (esp. good if you're planting a smaller area of X and Y than other veggies).
Maybe this will help.
Sunset Zone 17, USDA Zone 9