My school has quite a number of ipads in use by teachers and students. One student in my class uses his ipad constantly and my teaching partner is glued to his. I personally, do not have an ipad, nor do I have the desire to get one (at this time) but I do see their use in the classroom and so when I saw this post I thought I would share for any ipad lovers out there:
Technology Tailgate Blog has this list of apps on a budget
Obviously, since I don't have an ipad, I have not tried and tested these apps, but they are inexpensive and likely offer trials if you want to check them out.