I too am looking into a UNIX or Linux certification.
If you're going to go with a Linux certification I'd choose either the Sair Linux or the LPI. The reason for this is that both are vendor nuetral rather than being specific to one distribution. So you'll learn to administrate any distribution.
RHCE is specific to the RedHat distribution and won't help you out when you have to load software on a Debian box. Debian uses there own package manager rather than Redhats rpm system.
I'm going to do the Sair probably first. Then maybe the Sun cert. like Neo was talking about.
Sair course is about $1700.00 with New Horizons. Sun Certification is much more expensive. $5000.00 to get SCSA certified. I don't know about the prices for HP-UX or LPI yet.
Hope that helps.