When I was deciding where to put my vegetable garden, I picked the sunniest spot in the yard and started digging. I wanted to get a look at the soil. What I found was great soil for gardening, and some garbage left behind. Because some of the debris was painted, I became concerned about lead in my soil. Since I had planned to test the soil for pH, organic matter, phosphorous, and potassium I decided to add lead to the list.
Lead is a concern if your garden is near an older painted structure. To learn more about lead in soil, I recommend reading OSU Extension's 'Evaluating and Reducing Lead Hazard in Gardens and Landscapes'. If you do plan to have your soil tested for lead, we have a list of soil testing laboratories in the Soil Testing section of our Conservation Directory.
Some gardeners are interested in testing soil for pesticides. This is difficult unless you know what types of pesticides you are looking for, and even then it is very expensive (as much as $200/sample). Since the pesticides that stick around would be bound to the soil, I recommend washing your garden produce very thoroughly.