What is the plural form of "iPad 2"?
Solution 1:
Since iPad 2 is the brand name, the plural form would be "iPad 2s". A search for "iPad 2s" reveals over 500 hits while "iPads 2" yields only 80. Normally I don't care much for Google search results as an indicator for grammar, but in this case it appears that many of the "iPad 2s" hits are from official vendors and reviewers. However, there is enough room for doubt that you are probably fine spelling it how you like.
Solution 2:
According to Apple all their product names are adjectives and not nouns and so they cannot be plural or possessive. Here is an excerpt from their document Guidelines for Using Apple Trademarks and Copyrights
Rules for Proper Use of Apple Trademarks
Trademarks are adjectives used to modify nouns; the noun is the generic name of a product or service.
As adjectives, trademarks may not be used in the plural or possessive form.
Correct: I bought two Macintosh computers.
Not Correct: I bought two Macintoshes.
I guess iPad 2 tablets is correct. boo. :(
Solution 3:
In speech I would say "iPad [tu:z]", pluralizing after the numeral. However, I find all of the possible written representations of that to be somewhat unsatisfactory, so I would reword to avoid it. Simply say "iPads" if the context makes it clear that you're talking about generation 2, or use a circumlocution like "iPad 2 devices" or "iPad 2 tablets".
Solution 4:
Not Google but general intuition will make you realize that it should be iPad 2s and not iPad 2's (with the apostrophe).