What's the best process for backing up images from multiple cameras in one central location?

This is what I do:

Set up your computer as follows.

Set aside a folder for each camera on your home computer.
Purchase an online backup service that's suitable for the amount of data, operating system, cost and level of security you need.
Set up the service to back up photos from both folders.

Then, each time you attach one of your cameras to your computer:

1. Copy all the new photos from your camera's memory card to their respective folders.
2. Check your backup service - figure out which photos have been uploaded online.
3. Delete those photos that have been backed up online from your camera.
4. Disconnect and go out and take more photos!

This process has the following advantages:

Assuring that all of your photos (except the ones you have just taken) are stored in at least two locations at all times.
Storing it using an online backup service assures that the data is off-site. This means that if your house is robbed and your laptop and external hard disk and your cameras are all taken (which is very possible), you will still have your old photos.