Apps make the iPad extremely versatile but there are also a range of products to extend the physical capabilities of the iPad. What is necessary for you depends on what you want to do with the iPad. These are the most common types of accessories used.
Protection - the iPad does not come with a protective cover so this is the first, and probably the most essential, purchase to make. There are a wide range of covers available in an equally wide variety of colours, styles and materials from as little as $10 from online suppliers up to $100 or more with most around $40-60. Most importantly it must have a hard flap to cover and protect the iPad screen. It is very useful if the cover can act as a stand, even better if it will recline the iPad at various angles. Also useful is if the cover can put the iPad to sleep and wake it up like Apple's Smart Cover. A fairly useless accessory on sale are the thin plastic screen protectors - a good idea if anyone could apply one without bubbles. The iPad's screen is very tough and doesn't require this extra layer so don't bother with it.
Keyboard - this is a very common pre purchase thought but the onboard keyboard on the iPad is actually very good and is surprisingly easy to get used to. If however you really crave the physical keys in front of you then there are several cases available with a rechargeable bluetooth keyboard, you can even recharge the keyboard from the iPad by using the iPad USB adapter. Most standard USB keyboards will work with the iPad using the USB adapter in the Camera Connection Kit. As the iPad supports Bluetooth any keyboard with this function can also be connected. Carrying around a keyboard does defeat the portability of the ipad so don't bother, you'll find that the iPad's onscreen keyboard is more than adequate.
ATV2.jpgProjection - at some stage in school use you will want to project the iPad screen or student work and the most efficient way to do this is directly from the iPad. There are three main options. The simplest option is via Apple's AV Adapters ($45) that will connect directly into the ipad and mirrors any screen on to a big screen through a standard VGA or HDMI connection. Next is to use an Apple TV ($100) which connects to a TV or projector with HDMI input and will project any iPad from the class with the touch of a button - however it does not work (easily) through school proxies - please fix Apple. The third option is to use the Reflection App($15) that will mirror your iPad screen to any Mac or PC, wirelessly.
Camera and USB Connection - with Apple's iPad Camera Connection Kit ($35) you can download photos and videos from your digital camera directly to your iPad. The kit includes two connectors,
  • the SD Card Reader to import photos and videos directly from your camera's SD card.
  • a USB interface connector to attach your digital camera or iPhone using a USB cable - whilst not stated this connection will also allow other USB devices (keyboard, microphone, etc) to connect to your iPad.
After connecting, the iPad automatically opens the Photos app, which lets you choose which photos and videos to import, then organises them into albums. When you sync iPad to your PC or Mac, the photos and videos on your iPad are added to your computer's photo library.

There is a growing range of accessories being created to complement the iPad. The following are very specialised items that may be of value to those working in specialised areas.
tripodsm.jpgThe "Movie Mount by Makayama does things only a true filmmaker will appreciate: Attach a tripod to it for those pan & tilt shots, use 37 mm conversion lenses, including wide angle and zoom, add a video light or shotgun mics, or use an optical viewfinder when shooting in bright sunlight."

Original article . . . . YouTube video

ipad-handstand.jpgHandStand iPad holder - "a strap keeps the iPad attached to the han
d, leaving the other hand free. A rotating disk allows the iPad to spin from landscape to portrait. An integrated stand will sit the device on a slight incline for easier two-handed desk use."

Original article . . . . Youtube video
iklip.jpgThe iKlip is a multi angle microphone stand adapter for the iPad. "Securely position your iPad for optimal viewing and accessibility, while all controls, buttons and connection ports remain free from obstruction."

Original article . . . . YouTube video

irig.jpgAmpliTube iRig is a combination instrument interface adapter and g
uitar mobile software. "Plug the iRig interface into your iPad, plug y
our instrument into the appropriate input jack, plug in headphones, amp or speakers, download 'AmpliTube FREE' version for iPad, and start rocking"

Original article . . . . YouTube video
pixsticks.jpgPix & Stix is a set of capacitive drumsticks and picks for the iPad. Designed for use with Appleā€™s GarageBand app, the guitar picks and miniaturised drumsticks have electroconducive rubber tips for accurate, natural touchscreen pickup.

Original article . . . . YouTube video

omni.jpgUSB Hubs - synching iPads one at a time is a very time consuming process. Up unto now multi synching devices have been very expensive. SInce IOS 5 we now have wireless synching but If that;s not working too well for you then there is the Omni 24-Port USB hub is only $24.95 and will simultaneously synch up to 24 iPads. It will not charge the iPads but for this price that's not really a problem.
Omni . . . . . . 25 Innovative USB hubs