DDR3 memory modules that come with software to monitor the temperature the DIMMs. That's ... ehr ... a useful feature?
Crucial has taken one of their standard kits of RAM, attached better heat spreaders and hired a magician in order to get the RAM temperature viewable in a piece of software. The kit itself isn't all that insane in terms of performance, but the temperature monitoring will likely appeal to enthusiasts. If Crucial could broker some kind of deal to get this data included into mainstream overclocking utilities, they'd appeal to an even wider audience. Finally, they need to add shutdown, or alarm features if the RAM temperature exceeds a certain point. This would help extend the life of your RAM and give you a little confidence when pushing it to the limit.