In incomplete dominance, neither allele is complete dominant nor completely recessive. You can also run across alleles that have codominance. Polygenic traits are produced by two or more genes. An example of this is human eye color. Scientists have identified at last 10 genes that affect human eye color. Below you will find a video to cover each of these.
Take the time to watch the Brightstorm video, Codominance - Incomplete Dominance.
Another option is the Non-Mendelian Genetics video from Teacher's Pet.
Finally this video covers polygenic inheritance, https://youtu.be/gouqTq5p168