Linux/Unix is now more commonplace in the workforce, so Linux+ might be a good choice.
CCNA or it's baby brother CCNET (entry level, goes towards CCNA) would be another one, but you should have hands on experience with it.
For Microsoft, not sure if the MCP is still around, but passing one of the exams in the MCSE or MCSA certifications will give you a Microsoft Certified Professional (MCP) status. I did hear that they were discontinuing that though.
You could also go to Barnes and Nobles / Borders and look at the text books there... even the ... For Dummies books are pretty good. They will give you an idea of what you need to know.