As others have said, the CISSP is perhaps the most well-known and recognized IT Security certification out there. If you need to start more entry-level, CompTIA's Security+ is a good start, and actually can be used to take a year off of the work experience requirements of the CISSP.
After the basics are out of the way, the question you really need to ask is which certifying authorities are recognized and well-respected. Then, choose a certification from among those offered by those authorities which properly reflects your experience level and skill set.
The key to remember here, is that a certification should be exemplary of skills that you already posess - not just an exam that you can cram your way through. Before obtaining a certification, you should have at least some work experience to further demonstrate to potential employers that you actually have experience and knowledge in the subject represented by that certification.
The list referred to by @Rook covers a lot of territory. There's a number of certifications and organizations on there I've never heard of, but it also lists most of the big industry players as well.
- CompTIA offers a number of certifications covering several domains. However, most of these are very entry-level. The only Security-speicifc certification they have is Security+. Other certifications primarily focus on system or network administration and troubleshooting.
- (ISC)^2 is all about Information Security. They have several certifications available, including the well-known CISSP. A full CISSP certification requires passing a written test, five years of relevant and verifiable work experience, and endorsement by a current CISSP in good standing. If you fall short of the work experience requirement, you may hold the title of "Associate of (ISC)^2" until such time as you meet that requirement.
- EC-Council is most well-known for the CEH. Most of their other certifications also center around security and penetration testing, but there are some on other topics such as Forensics and Programming.
- GIAC was founded by SANS, which is a well-respected institute for security training. As such, they have numerous certifications covering many different aspects of Information Security. After obtaining a GIAC certification, you can also go the extra mile by elevating it to Gold status. This requires you to work with a GIAC adviser who will guide you through the process of writing a research paper (expected to take 6 months) which must be reviewed and endorsed by your adviser and two others in order to be accepted.
- Cisco is the go-to vendor for networking certifications. The most notable of these is the CCNA. They also offer some certifications which include a security focus. Their highest-level certification is the legendary CCIE, which requires passing both a two-hour written exam and an eight-hour hands-on lab which is only offered at ten Cisco facilities worldwide.
- Microsoft is, of course, where you want to go to get certified on Windows systems. Perhaps the most well-known, current certification is the MCITP - Server Administrator (formerly known as MCSA). Some of their certifications are also focused on security.
Full disclosure: I currently hold certifications from CompTIA, EC-Council, and Cisco, and am pursuing certifications from Microsoft and (ISC)^2.