Quote Originally Posted by Killa-Eyez
Solid state drive. Very expensive and not yet in big sizes but will last a lot longer..

Otherwise the above suggestions will do.
I'm sorry to contradict you, but SSD isn't really meant to be used as an external drive. That'd be a waste of money.
As for longevity, MLC SSDs and HDD might have a similar lifespan.

SLC ones, even more expensive than SLC would be the ones to have a much better lifetime, but they come in madly expensive prices for the storage space.

An SSD is meant for a system drive, and not any SSD, all Jmicron/Phison based are uber crap (eventhough expensive compared to HDD).
Then you have Indilinx based SSDs that are a leap from HDDs.
Then you have Intel at the top of MLC, and the uber drive in the X25-E range.
Please keep in mind Intel just had their postville drives out, a little more performance and "lower" price. That's for the X25-M range, the E range should follow.

Back the the question:
If data protection is very important, buy 2 external drives, have two copies for each important file, never connect both drive at the same time (electrically and to the comp).
Drives and enclosures from different manufacturers.
Most affordable, easy way to ensure some security to important data.

After that, it becomes very difficult to have the perfect, easy and affordable solution for data integrity