Hi- It sounds like you want to find something to help his speech. For help with learning sign language, there is the video series, Baby Signing Time which you can find online. It shows small children and babies doing the signs.
If you have an Ipod, Ipad o Iphone, there are applications you can download that are free such as Talking Tom which is a cartoon cat that imitates all the sounds your child makes. Therapists say that for beginning speech its really important to repeat everything they say back to them, even if it sounds like nonsense. Also, enunciating slowly and carefully in front of them so they can see your mouth and how it moves.
When buying toys for kids with Downs its good to remember that many of them have problems with coordination with their hands due to thicker, shorter fingers which makes it difficult to hold certain objects. General toys that are good for learning(depending on his skill level): Mr. Potato Head, Duplo blocks or regular ABC blocks, shape sorters, cars they ride on but push with their feet, toys that encourage make believe, such as kitchen playsets, etc.
Of course, keep in mind the best present is maybe a couple of hours of free time for the mom!