If you can afford it:
Put a bigger secondary drive in your computer (if you need the extra space), and buy 2x external drives that have the same capacity (or more).
Use the internal drive to store your photo's, and backup to the 2 external drives weekly (or after you upload a lot of files) using the operating system's Backup options, or a script such as Robocopy for Windows. You can configure these to backup everything, or just your folder(s) with the photos in etc.
Keep 1 external drive at your house, and put the other one at a friend/family members house (somewhere safe and secure).
Once a month (for example) take your current backup to their house and swap it with the other drive. That way you have a fairly up-to-date off-site backup.
Hard drives fail. It's OK having masses of storage, and even a backup. However if the worst happens and you have a fire or your computer/laptop gets stolen then there is little to no chance of recovery.
You can use "cloud" storage (i.e. online file storage) by the likes of Mozy Home (
http://mozy.com/home) or DropBox (
https://www.dropbox.com/) etc., however to get any decent space can cost a fair bit of money, and the initial backup can take days/weeks to complete depending on how much data you have to start with.
I have over 10 years of digital photos and converted video amounting to about 500+Gb. Now I have my new Nikon D90 this will only grow as the files sizes are bigger.
I am in the "lucky" position to have a server at home, but use the 2x backup drive routine to backup only the important stuff that will fit on to 2x 2Tb drives, and then keep one at my parents house.
Unlike many files - photo's are memories. If you lose your CV or a few media files you downloaded or ripped from CD's etc., it's annoying. If you lose photo's can you ever get back to that location and re-take them again?