What are the some notable Linux certifications?

Hi everyone,

I have to brush up on my Linux skills because of a job related issue... Although I want to start tackling the Microsoft certs asap... I can't just yet. I have used many distros in the past, Redhat, Debian, Slackware... but I've never really picked up a linux book and read it in detail. I just know what I need to know to get by and most of my knowledge came from Google and the man pages

Anyways, I would like to start studying for this and I might as well pick up some certs to keep me motivated. I was wondering what some of the most notable Linux certs are. Also if you have read any books, what do you recommend? I am looking to expand my knowledge in iptables, samba, q-mail and snort

Thanks in advance!