IT Security Website

I would make sure your developers are trained on secure coding, do a good Quality Assurance check for it all.  Implement a change control process to make sure all changes are documented and controlled, I would use some version control system.  Once you're live (or about to go live), have a penetration test conducted against it to find any holes you didn't catch previously.  You can request a redacted version of the final report to share with 3rd parties you want to work with (if your pentest vendor doesn't offer this, find a different vendor) once you've remediated the findings.

As said above, most of attacks can be  easily prevented if the coder/programmer used coding standard and security in the code, so write software that proactively implements parameter checking to insure that the vulnerability is not written into the software, which takes training and standards, and keep testing your software/application for the presence of  vulnerabilities. Additionally, make sure your web server is up-to-date with latest security fixes, Policy backups of the data would be a must, also implement WAF and firewall.

Thanks both. Would there be a list that you know of that I could check off as I go along and test?

I'm sorry, but there's no real good (or widely acceptable) checklist.  Here's what I'd try and capture:

Developers are well trained and practice secure coding

Change Management process and version control is in place

Firewall is in place and configured properly

IPS is in place and configured properly

Optional -- Site is tested by a penetration test, results are acceptable (critical, high, and medium findings are mitigated)