I've got a top of the range iMac 3.06 1TB with 4GB ram and the ati 4850
Yes its a great machine and does things well.. but i havent really had the wow factor from it.. seeing as its nearly £2000 worth!
Is there a specific type of game / program internet link that I could buy or access that will show off the iMacs prowess?
The WOW comes from the little things about OS X that surprise you and make life easier.
Here is one:
For example, create a new document inside TextEdit.app and save it. Then drag the little icon in the titlebar of the document window onto Mail.app's dock icon. You'll get a new email with your new document attached. If you right click on the same icon, you will see the path where you saved the file, and you can even click on of the the folders in that path to view it in the Finder.
If you want something to show off your iMac's power, try some games like Call of Duty 4, Oblivion, or others. I recommend getting the PC versions to play in Boot Camp because the Mac versions can be slower than the windows version.
Another way to get some of the WOW is to use some of the absolutely incredible third party apps like Delicious Library, PLEX or Boxee, Tweetie, Handbrake, Airfoil + Airfoil Speakers iPhone, Adium, and Quicksilver.
However, there is not much that when you show your friends, they will go WOW!