CISM it's for security managers, general security policies, security implementation stuff
CISA it's good for Security auditors, Penetration Testers. But not in the technical way this cert is good, but planning the audit, and all the procedures.
My chief from work has CISSP it's a general security related cert. also for security managers
.If you are more interested in the technical aspect of security i suggest C|EH (certified ethical hacker) from Ecouncil
Also the certs from SANS institute are good in the technical way of speaking.
I have CISSP and CEH. CISSP is useful as it requires 120 CPEs every 3 years on an "official" basis. It gives me cred to tell my boss that he needs to send me to conferences or training. CEH just started a CPE like system. Tests were generally easy, experience requirement was useful but doesn't mean you are proficient. As far as "gravitas", I think some people notice, but generally I could put any letters after my name and it would impress them. On that note, if someone has a CISSP, I know that reasonably I can talk to them about security issues - if they're not certmongers, they generally care about the state of infosec.
I don't know of any, myself... but ECCouncil's C|EH, E|CSA, and LPT would be a good start, for sure. The C|EH has a decent chunk of web app pentesting stuff. I would suggest those and a good amount of web app dev skills and web/db server administration (you can get individual certs in some of this) experience. Once you have the foundations, the web app pentesting is pretty much the same thing as os/application/network pentesting.
Now, keep in mind, I say all of this from a research standpoint, as I hold no certs and am still fresh on the infosec scene. I am only just now about to move up from minor sec admin/analyst tasks (policy/procedure, firewall, enterprise security, etc...) to QA/Web Sec and server auditing. :)