I was a spec ed teacher and had my students for 6th - 8th grade. I've been home since having my own kids, but I miss teaching! A few gifts that really meant a lot to me were ones that the whole class benefitted from.
One year a few parents came in and painted all my free standing bookcases in really fun colors (I was in an odd room that didn't have anything built in like most classrooms). These were bookcases that parents of previous students (before me) made for their teacher and time demanded they be painted again.
Another year a parent made me some organizers for posters, bulletin board stuff, etc - they were BIG file folder type things that she decorated and labeled nicely. I think she was also the parent that made me a wooden hanging file box that I used to organize each bell's work. I had an old cardboard one that was falling apart!
One parent made me a small scrapbook of pictures of her daughter's class over the 3 years I had them. This was before "scrapbooking" but she really did a great job decorating the pages. It included the official school pictures as well as snapshots taken over the years at all different school functions and activites. She collected pictures from all the kids. I kept the album in my classroom while I was teaching and future classes loved looking at it. I still have it.
I used a lot of homemade games in my classroom. Once I got a box filled with the types of materials I used for making games - file folders, manila envelopes, sharpies, glue sticks, index cards, etc.
You really develop a relationship with a spec ed teacher, so I know how you feel about doing something special after 3 years!