I'm a big fan of hybrid mattresses -- short springs for support and memory foam on top. The biggest advantage of this design is that you can easily move into different sleeping positions at night and you get much better spine support. The problem with most memory foam mattresses is that you sink into them (even the firm ones). The springs help with this.

After trying out numerous types, springs, gel, memory foam, latex etc. I found this combo to be my favorite. I haven't slept better and no more back pain from memory foam.

Serta, Sealy and Temperpedic (TEMPUR-Flex model) employ this design. Tempurpedic's Flex is a lot more expensive than other brands. I have a Sealy and love it.