iPad Gains Keyboard from Kensington
The KeyFolio offers some handy features, such as iPad-specific keys to access functions (such as home, etc.) and a stand that allows you to use your device much like a laptop. The battery within the keyboard itself must be charged; Kensington says it would last through about 90 hours of use before needing another charge.
It's not too heavy -- it only adds another pound or so to the overall weight. The keyboard is a tad small, think of it as close to netbook size -- a bit larger maybe, but still comfortable to type on.
If you're worried about the keys scratching the screen itself, don't. This is because the keyboard itself is rubberized -- a good feature too just in case you spill that cup of coffee on it early in the morning.