The one thing I'm still missing on my phone is the ability to use spreadsheets to track expenses. There are some webapps out there for this, but they don't really do what I need them to do. Is there anything else that can be used to create spreadsheets?
Files2iPhone (www.f2p.com) can do it, but it's not free--there is a free trial. It's not a native app (no jailbreak needed) but it does seem to be pretty good at editing remote spreadsheets. Benefit is that you are editing the document right on your desktop computer.
What I use, ironically mostly for expense sheets, is www.editgrid.com/iPhone. It has plenty of editing options. I actually uploaded a few XLS files (used my desktop PC) so the spreadsheets I use are my own. I grab them as needed when back to me PC.
I second editgrid. doesn't use the new 2007 excel file types but just convert to xls and it should work. It keeps all the formatting too AFAIK. But its a webapp so i don't know if you want something like that.