My friend Julie is an awesome Special Ed teacher. She got an iPad and wants to use it with her kids. I have a few suggestions. Please feel free to add your own!
First - here is a link to my classroom blog where my kids made recommendations about apps they like.
Probably my top recommendation for special ed is Dragon Dictation - this free app is a simple to use voice recognition tool, useful with reluctant writers. It does take a little getting used to and will require some punctuation editing, but it easily converts speech to text that can be imported to a word processor.
The (free) Kindle app is my favorite for ereading. I like the ease of looking up words while I am reading, as well as the ability to change font size, paper color and brightness.
Adobe Photoshop Express is still free and quite fun for creating effects on photographs. Doodle Buddy (or any similar drawing app) is nice to have for kids with motor issues.
Math Games - I use iPad with math centers. I am all about the free apps. Some my kids really enjoy include: Portion Platter, Mancala with multi-player support, NumberLine, Pearl Diver and Lobster Diver.
Language Arts apps I use with the kids include Hangman, Grammar Dragon, Bluster
Nicole Dalesio has a whole website set up about Digital Storytelling. She is awesome and has some great ideas.
Google Earth another free app I would certainly include.
Teacher Productivity tools that I use frequently include Evernote, DropBox and Splashtop remote.
Katie Stansberry posted on the ITSE blog, "Special education classrooms are finding iPads to be extraordinarily useful for language delayed students and individuals with communication challenges. Several Montessori teachers have even gotten involved with the new technology by building apps designed to tap into children’s natural observation processes and promote self-directed learning."
Scribd has compiled an extensive list of apps for Special Ed.
iPad Curriculum is a helpful site with some suggestions and useful search criteria.
For a limited time the Everyday Math games are free for iStuff! Get em while they are free!
Googling "ipad special ed apps" will get you about 1,190,000 hit so I hope this helps get you stated.
Finally, Appolicious is an app/website which provides info about Aps! Reviews, notification of sales, etc.