I have a 500GB Seagate external hard drive that came with Bounce Back Express software for doing the backup. You can set it for when you want prompted to backup. You also set up the files you want backed up. You can also just drag and drop files directly to it also if you don't want to use the software.

I like it keeps things updated and backed up.  I generally keep it unconnected and secured away from the computer. Each time it will look for new files and add them to what has previously been backed up. 

I'm leery of the on line backups. They can be hacked regardless of what they tout plus all your info is floating out there that others could possibly get access to. What happens when Carbonite and some of the other on line backups merge or go out of business ?  Do you really want to assume they will destroy all copies of your info or will they wind up in places (offshore) where you had no idea they would end up at.

Play it safe and take control of backing up your own data & information and don't ever trust or rely on anyone to keep your information secure for you.

My 2¢ worth

Here is a pdf link to the external hard drive I have and it mentions the backup software by CMS

http://www.seagate.com/docs/pdf/datasheet/disc/ds_external_pb.pdf

http://www.cmsproducts.com/products/backup_software/bounceback/bounceback_express.html