Do It Yourself (DIY) is a hot trend right now. Books, magazines and television shows are devoted to the topic. Here are some website that give helpful instructions for DIY projects for the special needs classroom.
Science Shareware has information on adapting toys. They also give the useful suggestion of enlisting scout troops to adapt toys.
One Switch, a long time favorite site of mine has directions for eleven DIY equipment modifications and more for adapting video games. Be sure to explore the rest of the site too, it's great.
Assistive Technology Partners has ten DIY project tutorials online.
Dale's Classroom Adaption does not have instructions, but the pictures are well worth perusing.
Do2Learn has DIY instruction to make a study tent.
The PVC Book is available in a PDF file and offers useful instruction to make all sorts of adapted equipment.
Braingle teaches us how to make stress balls.
Finally, intended for community based rehabilitation in the third world there is the United Nation Guide to Assistive Devices. Although you probably don't need directions to make a wheelchair or crutches, some of the ideas are useful and reading the document is mind opening. The article made me think more about people with disabilities in developing nations and what I can do to help.