There are the Linux Foundation certs, some of which (e.g. Certified Sysadmin) are well respected, relatively hard to get, and also very expensive. There are some cheap and some free ones as well, but I don't know if recruiters care about them at all. They are just a formal way of showing 'I know ' instead of you just saying it after all.
Depending on your domestic laws you may be able to deduct them from tax, or even get some kind of government subsidy for doing them. I would look into that if you wanna go after the really expensive ones.
There is also Red Hat, I don't know if those are worth it thought. Probably not the worst to have either.