The 1st question I have is how many people will be sharing the data on the NAS?
Once you have the NAS in place, consider backing it up and taking the data offsite...
Check out
http://www.smallnetbuilder.com for NAS reviews.
Based on the reviews on that site and others, I just put in AN order for a Netgear ReadyNAS Duo RND2110 from Fry's. It has 1 x 1 TB drive and has room for another (which I already have).
http://www.readynas.com/?cat=3
Brands to consider are QNAP, Synology, Buffalo, Netgear.
The above URL is the most comprehensive review site I've seen so far.
Cheers!