There are a few areas where programming comes in handy.  Malware analysis and reverse engineering come to mind.  As for your background with .NET development, have you considered focusing in Application security testing or Web App Security?  You may also be interested in exploit development. 

Also Microsoft currently offers enterprises the option to teach their devs about Web Application Security with .NET and ASP.NET.  I don't know if there are any particular certifications associated with it though.

From what I researched myself, Assembly is a big one to know if you want to reverse engineer.  Also knowledge of Python and C is probably helpful as well. 

For Analysis, there are a number of tools available and a nifty book - Malware Analyst's Cookbook

That will get you started with the analysis portion.  There are also some reverse engineering resources out there too.  I believe we have a forum section for that material as well.  Browse through there. 

As far as Certs, well you can browse the GIAC certs, they have one in particular for reverse engineering - GREM, SANS FOR610 is the related course.  You can browse the reference list of the course to get an idea of what you will need to learn.  Also Lenny Zeltser is a good person to follow on Twitter.  He has a decent site as well.

Aside from Malware Analysis and reverse engineering, exploit writing involves programming.  You can review the SANS curriculum for APPSEC to see if anything there interests you. 

That should get your started.  You can also do job searches based on the certs to see what the market looks like.