With the introduction of the iPad 2, I find myself hesitating when trying to refer to several of them. Is it iPads 2 or iPad 2's?
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.
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. :(
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".
People often pluralise "unusual" words with 's instead of plain s. Technically speaking it's considered incorrect (see "grocers' apostophe"), but I personally don't endorse that position.
A common example is when referring to decades/centuries. A lot of people write the 70's, for example (although even more write the 70s). That particular example may be influenced by the fact that people also write the '70s to indicate the missing century component, and no-one ever wants to put two apostrophes in that single "word".
In short, although some may say the usage is ungrammatical, I think it's just a matter of style.
The answer will be determined by popular usage, but it is likely to be iPad 2's.
The reason has been elegantly explained by Steven Pinker in his book, The Language Instinct (ISBN 0060976519). In one part of our brain, we store all the irregular plurals we know. When that fails, we apply a general rule we have stored elsewhere: for a plural noun, add -s.
This is why many people tend to use mouses rather than mice for the computer pointing device. To these people, it seems like a new word, so they automatically apply the general rule instead of recalling the irregular plural for the name of the furry creature.
Furthermore, when a person conceptualizes a compound word as a proper name for a thing, such as iPad 2, that person will add -s to the end of it and get iPad 2's, just as we would say Bill Clintons, never Bills Clinton.
Thus, because of the way our brains work, the plural form of any new proper name, even a compound name, will almost always follow the simple rule add -s to the end.
Let me also address the point made elsewhere about trademarks. Trademarks which function as brand names are adjectives: Ivory soap, IBM PC.
But a brand name can enter the language as a noun when people begin speaking of the thing itself using the trade name. For example, kleenex for a facial tissue was originally the trademark Kleenex tissue.
When this occurs, the trademark office actually does the reasonable thing and withdraws trademark protection for the term. It does this by the logic that you cannot have exclusive use of an ordinary word.
Companies are well aware of this. This is why their public relations offices will plead with the public to use their trademark as an adjective. They hope to influence the public to do so, because otherwise they will lose their trademark. And that is why Apple is on record stating that their trademarks are adjectives.