Walnut Substitution

pecans (not as crunchy or flavorful)
or 
hazelnuts (not as rich)
or
pine nuts (in pesto)
can be substituted for walnuts.

Pistachio Substitution

pine nuts
or
blanched almonds 
can be substituted for pistachios.

Pine Nut Substitution

walnuts (in pesto)
or 
almonds (in pesto)
or
hazelnuts (this also works in pesto)
or
cashews (raw, unsalted)
or
peanuts (unsalted)
or sunflower seeds 
can be substituted for pine nuts.  

Pecan Substitution

walnuts can be substituted for pecans.  

Peanut Substitution

cashews (stir-frying or for making nut butter)
or
almonds (for making nut butter)
can be substituted for peanuts.

Macadamia Nut Substitution

pecans
or
walnuts
or
almonds
or
cashews 
can be substituted for macadamia nuts.

Hazelnut Substitution

almonds
or
walnuts
or
pecans
or
macadamia nuts  
can be substituted for hazelnuts.