I usually keep the Scrum Product BackLog (PBL) on an Excel sheet and share it across the project members. It has its own pros and cons.
Some people also use Google docs spreadsheet for the same. I just found that you can also create a good looking PBL on Google Sites Apps.
The idea is to simply create a new page with List as a template
and then customize the list columns to show scrum pbl column’s.
Here is a sample customized list
and the sample PBL.
I think this could serve as another free tool for Distributed Agile team members.