Finding severe bugs after a release is 100 more expensive than before (2x for non-critical bugs), so how can more bugs be found before release? This [article][testing] suggests combining multiple testing/review methods, particularly adding code review:
> More generally, inspections are a cheaper method of finding bugs than testing; according to Basili and Selby (1987), code reading detected 80 percent more faults per hour than testing, even when testing programmers on code that contained zero comments.
So grab [mgunit][mgunit] and write some unit/regression/system tests; get a friend and have her look over your code; have a beta test period; etc.
[testing]: http://kev.inburke.com/kevin/the-best-ways-to-find-bugs-in-your-code/ "The best ways to find bugs in your code"
[mgunit]: http://mgunit.idldev.com "mgunit Trac site"