Yesterday OWASP released the OWASP Secure Coding Practices - Quick Reference Guide. This quick reference guide is a comprehensive checklist of possible actions to take. It isn't technology specific, so every developer is able to use it.
the Quick Reference Guide is release as a part of the OWASP CLASP project. CLASP (Comprehensive Application Security Process) is an alternative to Microsoft's SDL. CLASP integrates in to you development life-cycle and helps you identify security threats and measures in every stage of the life-cycle and as early as possible. I think this is a really solid alternative for SDL, so if you want to make your applications more secure you should take some time to study them both.
Here's the link to download the Quick Reference Guide.