Have you considered using Time Machine to backup your computer to an external drive? If you change the Time Machine backup destination in System Preferences > Time Machine, it will stop backing up to your Time Capsule, and backup to your external. Then once it has completed a backup to the external, just point Time Machine back to the Time Capsule.
[Carbon Copy Cloner](http://www.bombich.com/) is one of the best applications for this. It is free and makes a complete bootable backup of your hard drive to an external. I've used Carbon Copy Cloner many times and I highly recommend it.
SuperDuper! is another option. It allows you to create a fully bootable backup of your hard drive. The backup part is free, so you don't need to pay the $27.95 for the scheduling part. I've used SuperDuper! as well and it is a great application.