I generally keep things pretty simple and straightforward when it comes to my 2011 most-used accessories. I stick to things that enhance functionality more than form. I think Apple's done a tremendous design job and I tend to lean more toward items that add an ability to do something or improve some part of my workflow (or enjoyment). Here are a few of my favorites.
A simple, basic accessory that looks great on any desk. Since going case-less, I've really enjoyed the simple presentation of the standard Apple dock, and since the body of the 4S kept the same style, I'm still using the same dock I bought months ago. There are docks that do more, but very few look as clean and nice as this one.
This cool little dock is more of a travel item for me, though I do find myself using it at home too. It's a small USB plug that takes the place of your white cable and allows you to charge your iPhone standing up against a wall wherever you have an outlet. It has a nice, simple profile and is great to throw in a pocket or keep next to your bed and it works with your standard iPhone USB charger.
As I said, I've lost interest in casing my phone and have grown strangely comfortable with having it naked. Mostly. The BOOKback is the only thing I'll use on my iPhone. It adds a wonderful leather texture to the smooth back and adds almost no size or weight to the device. It's just thick enough to keep you from possibly using it with some accessories (something like a Mophie pack may not fit) but the standard Apple dock eventually accepts it after the edges of the leather break in.
This is something I wouldn't ordinarily find myself enjoying, because most of these kinds of things fall short for me. But the Bamboo is the first stylus I actually like. It's not perfect (for me), and my search for the optimal pen experience on the iPad continues, but it's a worthy addition to your bag for now if you like drawing or taking handwritten notes on your iPad. Works exceptionally well with a ton of apps, and feels great in the hand.
$29.99 - Amazon link
Quite possibly the most fun you can have on a tabletop with your iPad. Birthed from an April Fools' joke on ThinkGeek, the iCade sprang forth into existence, making many of my nerdy fantasies a reality. If you like classic video games, you must own this. It uses a Bluetooth connection to the device and is extremely well-constructed, making playing arcade games a joy. There's an SDK for developers to add support for the device, and more seem to be adding it each day, so it looks like this thing will be a part of my gaming experience for a while to come.