ksplice

It looks like the folks over at CloudLinux are looking to shake up the rebootless kernel update market with their introduction of KernelCare (http://kernelcare.com/).  They announced pricing on March 30th, with retail sales starting on the 1st, so it's a newer solution, but looks promising...

Read this the other day, has anyone tried it before on production? http://korovamilky.tumblr.com/post/16460518079/running-new-linux-kernel-without-rebooting