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.