A good place to start is the Robert Half Technology 2011 Survey. Not only does it provide salary information, it also provides information on what certifications are in demand. According to the research, the following certifications are in high demand:
Cisco Certified Network Associate (CCNA)
Red Hat Certified Engineer (RHCE)
Microsoft Certified Applications Developer (MCAD)
Microsoft Certified IT Professional (MCITP)
Microsoft Certified Systems Engineer (MCSE)
Microsoft Certified Technology Specialist (MCTS)
Project Management Professional (PMP)
Certified Information Systems Security Professional (CISSP)
Check Point Certified Security Administrator (CCSA)