Flexible Solutions, home of fellow MVP Victoria Yudin, has a new solution out for accessing Crystal Reports from within GP. I have to say that the interface and options shown on the demo video look great. The product includes parameter handling and mapping, the ability to tie a report to the printer icon on a window and report grouping. If you use Crystal make sure you give the demo a look.
Crystal Reports from Within Dynamics GP
Archived post from 2008. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.