I don't know the first one, but the bottom two - CISSP and CSSLP - are both certifications I have. Neither one is going to give you enough specifically web security related information to make you into a knowledgeable web security developer. CISSP is a very broad certification where the qualifying candidate is expected to know a little bit about a very wide spectrum of security techniques.
CSSLP is a bit narrower - its specifically focused on software, so the candidate is expected to know a smaller subset of the CISSP topics, in more depth. There will be good software security stuff in there - stuff that is applicable to the web as well as any other software product. Again - not specifically a "web security" certification if that's what you're after.
In prowling around the ISC2 website, did you make to this page?
Filling that out for the CSSLP will get you exactly what the CSSLP cirriculum is these days. When folks are studying for these exams, they live and die for the "CIB" because it's the most up to date, bottom line description of what's going to be on the exam.
Unfortunately, I got myself a CSSLP before they implemented the test and cirriculum, I was in a lead batch of people who were certified to give the certification some street cred - so I can't speak much to whether I learned anything interesting the course of studying.
I can say that while CISSP has gotten a strong foothold in some industries, the CSSLP hasn't. ISC2 has a good reputation, but I haven't seen the strong push for CSSLP certified developers. IMO, that's because there's a big enough foot hold of generally good ways to interview for programmers, that the risk is not high that you'll hire a dud. But for security wonks, it's all over the map, and an organization typically only hires one or two - so CISSP ratings are much more helpful.
My biggest critique is that this is NOT a hands on course. If you thought you'd be staging, hacking and protecting software as part of your coursework -- think again. The course will prepare you to do well on a multiple choice exam. It'll have a lot of good information, but the application of the theory will be left up to you. Another tip - ISC2 produces courses and other companies produce courses. Look around and see what curriculum works best for you. ISC definitely structures courses for the CIB, I can't speak to other companies, but I've seen plenty of books labeled CISSP that where only tangentially related - your best bet is to compare the CIB to the cirriculum.
As an interviewer, my reaction is - a certification proves that the guy can take a test. Interviewing is the better indicator on whether the guy can do his job. I don't need him to take a test, so he better be able to talk about actual work that he's done (in the classroom or the cubicle) when we do our interview, or I don't care WHAT certification he has! Mileage varies only slightly in a world where my customers are demanding certifications... then I may be forced to keep searching until I find those guys that can do the job AND have certifications. But if I have to choose, I'll take the guys who knows how to do the job every time.