Ipads.
Web 2.0 presentation from Joe DaleA classroom 2.0 presentation and a live binder from Joe Dale. Joe is very good in the eLearning sphere, and there is no point in reinventing the wheel. However you may also want to look at the computer science page, where I have listed some resources for building Apps.
Android
This could be a cheaper option, and is part of a more open ecology. Here is a link to an edudemic recourse page on deploying android tablets.
Android in the classroom
Microsoft Surface tablets
Its cool, its different, it has lots of connectivity, it has a good pedigree, if you think Microsoft is a good pedigree, and its not a cheap option. My personal thinking is that its still too early to make a call on this, as Microsoft let the sdk out to the developers rather late so that there are not currently many slick education apps for this available, hence the poor reviews it has been getting in some quarters.
Hagiography an early review(Edudemic)
A windows tablet in primary
Bill Gates on keyboards Bill gates has a good point to make in this interview.

There are two other alternative paths that schools should consider before going down the tablet path with a one size fits all solution.
1) Bring your own device,
2) Netbooks.