I'm learning for LPI level 1 certification.
It's a vendor neutral, worldwide valid certificate, which shows you can admin a Linux system with around max. 10 users or so. And your employer can check online if you indeed have the certificate. Also, I found books at bol.com specially to prepare for that exam.
At the moment, in South-Africa, 200 people are being taken off a mass-exam for this certificate, just to mention something of the world-wide interests in it (I live in the Netherlands).
The advantage of some vendor neutral thing is, the one who provides you the certificate isn't a company just trying to earn money from you. Normally, vendors let your certificate expire very soon, and send you a letter telling you should do the exam again, which means revenues again for them, and sometimes almost nothing changed between the two exams. LPI-certificates are 'active' for ten years for now.
Only problem is, most employers don't know the LPI certificate. But since it's vendor neutral, you can say you can work with Red Hat, Suse, Debian and so on.
The costs are about 125 dollar per exam inc. vat, depending on the vat of your country.
For more info,
http://lpi.org/en/certification.html