"Meteor-wrongs": Here at the Cascadia Meteorite Laboratory, we frequently see samples that lay-people believe might be meteorites, but which are not.  Below is a list of common "meteor-wrongs".

SLAG: Slag is a nonmetallic product of the smelting and refining of metals. Slag can have shiny surfaces (left) or a bubbly texture (right).
 

IRON OXIDES: Weathering of iron-bearing rocks on the Earth can produce iron oxides (hematite) and hydrated iron oxides (limonite/goethite). Hematite (top left and right images immediately below) often has a silvery or reddish-brown exterior, and always will leave a reddish-brown/maroon streak on a ceramic plate.  Limonite (lower left and right images) typically has a brownish or mustard-colored exterior, and always will leave a yellow-brown/mustard streak on a ceramic plate.  The picture in the upper right shows hematite that has replaced pyrite, retaining pyrite's cubic crystal structure.  Meteorites will never have cubes or rectangles sticking out from their surfaces.