I would not get any of the pre-packaged solutions that are available today. I just think they cost too much ad offer too little (IMHO). I would get a very good enclosure that has SATA II, Firewire 1 and 2 (also called 400 and 800) as well as USB. I would then purchase some size SATA hard drive to put in the enclosure, such as a Seagate 1 or 1.5TB drive (I use both). The best enclosures on the market go for $70 to $90, but others can be had for as little as $20. I prefer the high end since it gives me what I am looking for, besides I also like the metal case. The hard drives when on sale could be as little as $99 for 1TB or $129 for 1.5 (I actually purchased my last 1.5TB drive from newwegg for $119). It takes about 5 minutes to assemble this solution as it is just a matter of connecting the HD to the Sata cables in the encolsure putting 2 screws in and plugging the enclosure into power. Then select the cable you are going to use.
Now depending on what you are trying to do this is where things get interesting. If you are only trying to save user created data, and not programs and such things it is easy. I prefer to mafe a folder called DATA and always store everything I create there. I even force Outlook PST file to this folder as well as making it my default location for programs such as word excell and Powerpoint. By doing this I then only need to copy this one folder to the external drive. You could then even create a Mrs and Mr Data folder and be done with it.
Now for the really paranoid you get a utility program with Seagate or Maxtor drives that allows you to clone the original drive. This is handy since it copies the entire HD including MBR (Master Boot Record) to the new drive. This will allow you to copy everythin and it is pretty fast, I have copied a 300GB drive about 60% full in less than 1 hour. It is also handy if you are trying to upgrade a HD in say a notebook computer.
I do not have the adversion to 2.5 inch drives someone stated since these are standard notebook drives. I have done everything listed above with 2.5 inch drives also. But it all comes down to using a good enclosure and a good drive.
Like you I do not send anything over the net. Besides the security aspects (which I would overcome with encryption), the time required and size required for me would be too much. I do have a safe where I have a master hard drive stored, and all my hard drives have at least raid-5 protection and in some cases raid-1(morroring). Oh, and by the way the critical data is stored all every raid set so a complete failure of a raid group would not harm me.