There are several way, but the two that I use are Pages and Documents to Go. So far, I haven't had any problems with Pages. But, I haven't worked on any real complicated documents. I am hoping Dataviz updates Docs to Go for the iPad screen.
I use pages quite a bit, and have signed up for the iWork.com beta. When i finish a document for class, I just click share via iWork.com and send the email that pops up to the teacher, he can then go to the link and download it as a pages file, a PDF, or a .doc file. Early reports from my teachers say that the conversion to PDF isn't perfect, but the doc files come out fine.
The iWork.com solution sounds like one of the workarounds for the lack of direct print capability. A perfect world would permit us to print directly from the iPad using Pages or Documents to Go. Hopefully that day will come.