Pro Softnet Corp. has released IDrive Portable for Mac (http://www.idrive.com/portable/mac_download.htm) that allows for a "quick and easy" backup of a Mac to a portable drive. It's an external drive that can be plugged directly into your Mac and works right off the box since it comes preloaded with the IDrive Portable backup software. 

IDrive Portable is comprised of features such as automatic selection of your most commonly used folders for backup with options to customize, multiple Mac backup, search for backed up data, and Smart Sync. The latter brings the data on your portable drive in sync with that on your Mac, mounted drive backups, an intuitive interface to select files/folders, etc.

The US$69 IDrive Portable drive comes with 320GB of storage space. That's enough space to carry almost 10,0000+ pictures of your Photo library, 150 hours of your favorite videos, and almost over 10,0000+ hours of your favorite music on iTunes, says Gokul H, designer at IDrive.

IDrive Portable for Mac is a free software download and can be used from any portable drive. All you need to do is transfer the IDrive Portable package to the external drive and install.

For additional security, a secondary backup is available through IDrive Online Backup for Mac.
IDrive online Backup for Mac offers 2GB free online backup with advanced features that include scheduling and quick incremental online backups.