What are the security concerns I need to consider while coding?

Question

I know SQL Injection is one... what are the others...

Answer 1

Here is a list of Top 10 Secure Coding practices. It is as good a start as any. Consider #8, Defense in Depth, in particular.

Answer 2

Sending plain text passwords without first encrypting them is never a good idea.

Answer 3

You could consider the chapters of this book to be a pretty good checklist...

19 Deadly Sins of Software Security