Some other good examples are snow plant (Sarcodes sanguinea)[1] and phantom orchid (Cephalanthera austiniae)[2]. It's also probably worth mentioning that this is an example of symbiosis in the borad sense. It's not a mutualistic relationship where both the fungus and the orchid benefit. The parasitic plant is using the fungus essential as a straw to suck sugars and nutrients from the roots of other plants. The fungus does not appear to gain in any way from the relationship.

[1] http://en.wikipedia.org/wiki/Sarcodes

[2] http://en.wikipedia.org/wiki/Cephalanthera_austiniae