It was interesting going back to using a desktop machine, because I've grown accustomed to the large trackpad built into MacBooks. All iMacs come standard with Apple's wireless, compact keyboard and wireless Magic Mouse -- and it became clear the Magic Mouse may not be the best option if you plan to upgrade to Mac OS X 10.7 "Lion" when it is released later this month. Lion offers more in the way of gestures, which work well on a touch screen or trackpad, but don't translate well when you're using a mouse.
You might want to use Apple's available Bluetooth "Magic Trackpad," which is easy to set up on your desk and provides a stable platform for using sweeping gestures or intricate mouse movements. I've used the Magic Trackpad, and I'm really impressed by it; given that Lion really takes advantage of the multitouch technology and incorporates swiping, pinching and other gestures, you should consider getting one to go with an iMac.
On the other hand, the keyboard -- while large enough for most users -- may feel a little cramped for larger hands. It's by no means netbook-small, but the overall size makes it feel that way. (Apple did away with the extended number pad found on most keyboards a while back, so be forewarned if you expect the extended keyboard.) I never had a problem with the battery life of either the mouse or the keyboard, but if you want a full-size keyboard, a full-size aluminum keyboard -- with number pad -- is also available, though it's not wireless. You can choose it, instead of the Bluetooth keyboard -- or the Trackpad instead of the Magic Mouse -- at no extra cost when ordering the iMac from Apple's online store.
Options to consider
Upgrade options abound: As noted earlier, you can bump the processor on the $1,999 model to a 3.4GHz Core i7 quad-core processor. Memory can be upgraded to 8GB on all models, or to 16GB on the high-end models (for $600 -- ouch); and you can add a 256GB solid-state drive for $500. In fact, you can combine the SSD with a 1TB or 2TB hard drive disk for both speed and storage space. The last option is expensive, adding $750 to the iMac's price, but you can't beat the dramatic increase in responsiveness.