Umami

The fifth flavor; it is sensed by specialized receptor cells on the tongue which detect the presence of glutamates.

The best way to describe it is "savory" or "meaty", and it is a major part of virtually every world cuisine except it took till 1908 to identify it conclusively.

Here's a brief list of foods high in "umami":

aged Parmigiano-Reggiano (off the charts, actually!)
aged blue cheese (in general)
anchovies
nam pla (Thai fish sauce)
fresh tomatoes
tomato sauce (with salt -- read below)
boiled potatoes
mushrooms (particularly shiitake)
fresh oysters
fresh clams
dry-aged steak (the only kind the CC will eat)
kelp (konbu -- which is where this was first detected.)
katsuobushi
soy sauce

The flavor is particularly enhanced in the presence of salt, the glutamate ions, and the Na+ ions work in conjunction.

Hmmm... looks like the CC's taste buds are particularly zoomed in on this taste.