iMac G4. I see many has voted for this one in this thread, and for good reason. It's design is mindblowing, even today.
iPhone. Yes, there's some flaws in it's design (chrome bevel? Who thought that one up? And the ugly black bottom (yes I know it's necessary for the phone antennae)), but as a whole it's just mindblowing. The first time I took it out of the box and held it in my hand, it's just unbelievable how sleek and cool it is.
And finally, the one that held it all together... OS X. Best operating system ever.
Honorable mentions:
1G iPod nano. It was so sexy even I wanted one! (I'm Deaf)
PowerBook G4 Titanium. When I first saw it, I decided to switch to Macs. Yes it was that good.
PowerBook G4 12". It's an awesome sight to see. I wish they didn't drop the 12" from the MacBook Pro lineup.
MacBook Pro. The dumpage of the 12" withstanding, it's an awesome design, being the first with a built-in iSight, and all that stuff from the aluminum PowerBook G4s.