Storage

As I look into the future to try and anticipate what our organization's greatest needs will be for the next few years one of the topics that always floats to the top is storage. In the short time that I have been involved in Church IT I have found that people use as much storage as they can get. Granted our storage strategy has been fill it up and we will go find some more. We currently have a little over 1 TB of storage spread across several servers. Currently we are a single site church and we even have the luxury of housing our administrative offices on site as well. This means that we are all on the same switched network. My mind keeps pointing me toward some kind of large storage device such as an NAS or even a SAN. I would like to provide enough space to the users that is easily expandable so I can get the storage problem off my mind for a while. The only problem I keep running into is once I have this massive amount of storage how am I going to back it up and get it off site.
Sorry but that is the end of the thought and instead of something insightful I leave this post with a question: How do you get offsite storage of multi-TB's of data? Even better how can users classify their data so we are not backing up the stuff they don't even remember what (or where) it is?
Tricky.