I can't believe no one has mentioned BuffaloNAS yet. It rocks. Plus you get RAID with it.
If you are just looking to be able to access files from anywhere then I highly recommend a BuffaloNAS device.
I have the 2 TB (yes, that's correct) model running in RAID 0 configuration. Essentially the drive has everything duplicated on separate hard drives so if one goes bad you do not lose data. You can get larger devices running up to 6TB I think.
The best part is that you can map drives to it locally like a file server AND access it over the internet by going to
www.buffalonas.com and entering your unique key you setup when you set up the device. You can also set up multiple keys so your friends can be "read only" and you can have full rights.
All that for under $300. Just google "Buffalo NAS" and thank me later.