Cisco
Covering Cisco Systems internetworking hardware and the Cisco IOS. Includes: CCDA, CCENT, CCNA, CCNP, CCDP, CCIP, CCSI, CCIE, CCSP,and more...
Citrix Systems
Covering Citrix products and architecures. Includes: CCA, CCEA, CCIA, CCI
CompTIA
Popular foundation-level vendor-neutral certifications covering specific technology areas. Includes: A+, CDIA, i-Net+, Security+, Wireless+, e-Biz+, Project+, Linux+, Network+, Server+, CTT+, and more...
ISACA
Popular infotech information risk management and auditing. CISA, CISM
ISC2
Vendor-neutral security certifications. Includes: CISSP, SSCP, and more...
Microsoft
Certifications covering the Microsoft operating system (Windows 2000, .NET, XP) and software. Includes: MCP, MCAD, MCSA, MCDBA, MCDST, MCITP, MCPD, MCSD for Microsoft .NET, MCSD on Microsoft Windows 2000, MCSE, MCT, and more...
Novell
Certifications from the people who brought us the first real computer certification program. Includes: CNA, Novell Specialist, CNE, CNI, MCNI, and more...
Oracle
For Oracle database administrators and developers. Includes: OCA, DBA Certified Professional, Oracle Certified Internet Application Developer, Oracle Forms Developer, OCM, and more...
Red Hat
Hands-on Linux certification. RHCA, RHCE, RHCT, RHCSS
Sun Microsystems
Certifications on Java programming, the Sun Solaris operating system, and other Sun technologies. Sun Certified Engineer for Sun ONE Application Server, Sun Certified Java Programmer, Certified Solaris Administrator, Mobile Application Developer, and more...

"The course broadened my horizons with respect to hacking, and the breadth was quite amazing."
Guy Merin, Research and Development, Microsoft