Have you started compiling your holiday wish list yet? Here's one item I'm definitely adding: the ThinkGeek TK-421 iPhone Case with Flip-Out Keyboard. (Bonus points for anyone who gets the "TK-421" reference--curious as it may be.)
I know plenty of people who don't like the iPhone's onscreen keyboard. The TK-421 offers a tactile alternative, one that rotates out from behind the case when needed and then tucks away again when not.
ThinkGeek doesn't provide any dimensions for the case, but it'll obviously add some thickness to your phone, along with a side protrusion that houses the hinge.
The keyboard itself is powered by its own rechargeable battery, which charges via USB. That sounds like an added hassle to me, but I suspect its power draw is very slight, so hopefully you won't need to recharge very often.
What connects the keyboard to the iPhone? In a word: Bluetooth. That's good, because it eliminates the need for any kind of dock connector--but also bad, because it leaves out iPhone 3G owners. (Apple decided against adding Bluetooth keyboard support to that model.)
What do you think? Cool design? Reasonable price? I could definitely see myself using this, but ultimately it depends on the quality of the keys. If they're comfortable, fantastic. If not, well, I'd probably exercise ThinkGeek's 30-day money-back guarantee.