Whaa? I defended you! I feel betrayed!!
It sounds like you want more of a what-can-OSX-do kind of thing in which case iLife's definitely the first port of call. IPhoto's Faces and Places features, when set up, are pretty impressive. Showing someone how simple it is to create a simple web presence with iWeb and adding a MobileMe Web Gallery with your iPhoto pictures with just a few clicks is pretty impressive too. Get things like Expose set up pronto to screen shortcuts (I use top right for show desktop, bottom right for show all windows and bottom left for dashboard), people love the look of that and are often impressed with the Dashboard. After a while the dashboard quickly loses its novelty but it becomes a great tool for quick access to a calculator, dictionary, thesaurus, translator, currency or anything else converter etc.
Another great program which I find impresses people is
Delicious Library. So easy to use and the barcode scanner thing is very impressive. You'll spend an afternoon scanning all your books, dvds, games, cds etc in but once you're set up you've got an instant access for everything. Great for keeping track of what films you've lent to who and also as a general backup of all you own. So if you keep that one database file backed up somewhere then if you get burgled you'll have a list of everything for the insurance company.
VMWare Fusion or Parallels is another good tool for convincing people that they could live with OS X instead of Windows so that might be worth a look into. Its pretty cool when you use their Unity type interfaces, in Fusion at least.
Other than that, make sure you have your bases covered on compatability type things. So download the Perian codec pack, Flip4Mac and VLC. Growl's a very useful plugin used by loads of things. I know codecs might seem a little boring but it can easily kill the WOW factor when you try to open up a simple video file that would have played fine on Windows only for it to fail.
To be honest, as others have said, the biggest WOW factor will come from the look of it. People are amazed at the size of Apple's displays. You'll quickly get used to it but visitors won't. A friend dropped round at mine a few days ago with another guy because he didn't own a printer and had to print something as a matter of urgency. The guy was speechless when he saw my 30" screen. I bought this screen nearly three years ago! The same goes for 24" screens, most people from the PC world are used to 20" or smaller.