Software Testing
If releasing a relatively bug-free product is important then having a team of software testers is key. It is true that the developers developing the software should do some testing, but they are too involved with the application to be able to put it through a rigorous test regime. The good software tester is able to suppress any thoughts about how a user "should" use an application and instead comes up with all the ways that a user "might" use an application. All of this is geared towards identifying unhandled errors before an application gets in to the hands of a user.
Typical Roles