This is a good resource to help us in the beginning of the year to build subitizing for both Perceptual Subitizing (recognition of number patterns) and Conceptual Subitizing (recognition of number patterns parts to the whole). When you use the dot cards with students you should ask "What do you see?" as opposed to "How many?" It gives the children the opportunity to think about the dots as different arrangements of numbers. (Dr. Nicki Newton)
More cool subitizing resources: MovieMakers.