Final Cut HD Pro (pro video editing), iLife (seamlessly integrated consumer media production and management, free with every Mac), Xgrid (instant, easily-managed clusters), Logic Pro (pro audio creation), Xsan (ultra-cheap SAN creation and management), Remote Desktop (haven't seen anything that good on a PC), and of course there's OS X itself.
Whoops, I think I went a bit over three, and I included titles that cater to the consumer, the pro, the scientist and the systems administrator.