The pebble bed type of reactors, for example, can't go into meltdown like the traditional types do. (
http://en.wikipedia.org/wiki/Pebble_bed_reactor)
And to say "you can't switch it off" about the traditional reactors isn't really accurate either. In fact, all of the Japanese reactors involved did "switch off" as soon as sensors detected the vibration of the earthquake. Control rods stopped the nuclear reactions from happening. The whole problem is dealing with cooling everything down AFTER it's "switched off", because there's still a lot of residual energy to be dealt with.
I think moving forward, there are certainly safer ways to construct new nuclear reactors, but you're simply not going to see all the utility companies of the world disassembling multi-million dollar investments in existing reactors and scraping them, simply because new, safer designs are possible. They need to stay operational at least long enough to generate a payback on their initial investment.
So in the meantime, I think the reasonable thing to do is look at ways to address cooling and redundancy for it. The Japan crisis illustrates how their existing setup wasn't redundant enough to give them enough options.
