MCSE (Microsoft)
CCNA (Cisco Certified Network Associate)
CCNP (Cisco Certified Network Professional)
CCDA (Cisco Certified Design Associate)
CCDP (Cisco Certified Desigh Professional)
CCIE ( Cisco Certified Internetworking Expert - ISP or Routing and Switching or WAN Switching)
MCNE (Master Certified Novell Engineer)
There are more types of certifications available but I am listing the ones most commonly sought.