Apple has published a 705-item list of applications that have been ported to run as Universal binaries.
Universal applications will run happily on Macs based on both Intel and PowerPC chips. PowerPC-only applications must rely on Mac OS X's Rosetta emulation layer, which lets most software run, though subject to a slight performance hit.
Apple's list includes software made in house by the company, and also a host of applications from thrid-party publishers.
The list is searchable. Apple is inviting developers to submit their Universal applications to be added to the list.