If you feel that you have developed a strong record with this organization in the two years that you've worked for them, then it's time for you to speak up for yourself. Salary negotiation is scary, and it takes both confidence and preparation in order to do it right. You've gotten off to a good start by investigating the average salary for CS graduates. You can find out just how much someone with your training and education can command in your field. One thing that I suggest you do is talk with someone in a professional organization, such as the Association of Computing Machinery .
Professional recruiters are good resources, too.
The second thing that I suggest you do is get your hands on a copy of Negotiate Your Job Offer by Mary B. Simon. This book has a number of exercises that teach you how to begin and end the negotiation process, including a self-inventory section, a preparation section and a communication section. Usually, I recommend this book to people who are in the interviewing stage of their job search, but I think it would be helpful for your situation as well. I admire your loyalty toward this organization, however, you have to ask for what you want. Don't expect the company to give you more if they can get away with giving you less.