Two of my favorites are the most recent Canadian Maple Leaf and the British Britannia, (both with the security background) but I'd have to say that the US Buffalo is my absolute favorite. It has it all: great looks/detail, numismatic history, 24K.
A 1oz Eagle is a great choice too. In Canada the Eagle is too expensive to buy from a dealer because it non-pure, which makes it a taxable purchase. That prevents me from owning them.
The Mexican 50 Peso is a nice, hefty coin, but at 1.2oz of gold it's pricier than others.