First let me confess: I'm shocking at getting through sorting and processing my shots. It takes me ages, and I always have a huge back log. In fact you can expect that I could throw up an image from years ago that I've just got around to looking at properly. It's so back that of the roughly 500GB of space my photography directory takes up, 300GB is in the "new" folder (yikes).
Regardless, that makes 200GB of shots I've got sorted, processed (sort of - some of my earlier shooting is not well sorted). I use 1TB portable USB drives for backup. I have one in QLD, and one in Tassie. Whenever I migrate, before I leave, I update the local one and hide it away. The problem is that there are big time gaps between the updates. I've wanted an online solution for backup - but have always found them too expensive..... until now.
Amazon offers a very cool service called Glacier. It's purpose built to hold data that does not change - so it suites my sorted images perfectly. It's got some caveats regarding retrieval in the event that something goes wrong (it can be slow, and costs if bulk retrieval needed). However, it's super cheap (1 cent per GB per month), and super durable (99.999999999% availability).
The only downside I've found is that since it's in the cloud, it's dependant on a decent internet connection. In Tassie, we normally stay a fair way out of town so we only got 2.5MB/s over ADSL. Not great - but I had an unlimited plan, and could just let it run as long as it took. Here in QLD, we're in one of the fastest growing suburbs in Australia, and there's not ADSL! Seriously - I'm in a complex of 30 units and can't get ADSL (to far to the exchange). Last year we stayed in the complex behind this and couldn't even get testing phone lines - because there was no spare ports at the exchange! I've written to the local member here, but may as well have shouted my problem at the wall - no response whatsoever.
Anyway... back on topic. Try Glacier - it's awesome. I'm using the FastGlacier client, and while I haven't gone through all it's capability, and its done a great job so far.
Final Note: my IT background means I still very paranoid about data saftey. As I tell folks: data is always trying to escape. So I'm sticking with my dual USB drives as well.