I would recommend DocsToGo. It costs $20, but I think it's completely worth it if you want to use your iPad for light document processing. I'd also recommend getting a separate keyboard.
I believe there is actually a mini-Microsoft office available as well. I haven't used it personally, but heard good things.
Also, I love iPeriod.
This is the first time in my life I've had any idea when I'm cycling.
iBooks is great, but Kindle has more books available.
The newsstand is great too! Those are built in. The iPad is pretty fabulous even without any apps!