I am not entirely sure what you mean by ``store files''. If you are concerned about losing data due to user error or software issues, a good backup strategy can do wonders.
For the home user, a cheap option would be one or preferably more external drives, which are only connected to the PC and Power grid when the backup is in progress. A more sophisticated, but much more expensive setup would be a tape drive. It is certainly more reliable since tapes are less susceptible to damage from dropping or handling in general.
I run a Linux server with a bunch of HDDs. It is read-only for the network and uses rsync to grab copies off the most recent file versions from my file server.
If you are concerned about the storage medium mostly, I would rank them in the following order of decreasing reliability:
- flash
- optical media (DVD/ CD), which are refreshed on a good schedule
- tape
- optical media (DVD/ CD)
- hdd
- floppies and the like