The Linux Professional Institute provides certifications in the area of Linux computing (no, really?! Lol)
The cool thing about the LPI is that they are distro agnostic, which is something I have been looking for as I would hate to get distro x certified only to find that whatever project comes up requires me to have knowledge of distro y.
Having a thorough understanding of Linux in general will be more beneficial in the long run. Any distro specific stuff can be learned as and when I am using that particular distro.
The LPI currently offers four certifications:
1.) Linux Essentials
More details can be found here: www.LPI.org
I just downloaded the Linux Essentials e-book, which has been made freely available under the Creative Commons license.