Touring: Longer chainstays to accomodate rear panniers and give more stability under a load. Cantilever brakes and clearances for at least 32mm tires and fenders. Lots of eyelets for racks, fenders, extra bottles, even little holders for extra spokes. Gearing is typically lower - 48/38/28 in the front with a wide range cassette (11/32) in the back. Often uses an mtb drivetrain. Serious touring bikes have downtube instead of STI shifters. Almost always has a steel frame.
Cyclocross: Road bike geometry for the most part. Also takes cantilever brakes and has clearance for big tires, often really big. Might have cross levers for the brakes, and may have downtube shifters. Frame will usually be aluminum but a few models are steel. Gearing more like a road bike with a "compact double" - 50/34 in front. Cross bikes usually have eyelets for racks and fenders since they are often used as commuters.
Technically touring and cross bikes are road bikes since they both use 700c wheels. If a frame has cantilever brake bosses and takes a 700c wheel, then it's a cross or touring frame. If the fork has little holes halfway down on the outside, then it's a touring bike.