There's an option, to show the wire, even in "solid" mode.
It's in object mode the object (F7) tab

subtab "Draw" (the third from left)
There, you can set the maximum drawtype (the highest quality of the object, that'll be shown)
Then, you can activate "Bonds" (in different modes: Boundingbox, -sphere, -cone, -cylinder and "polyhedron", which doesn't work for me)
Texspace
Transparency (based on the Alpha value) - if you have parts in the mesh, that overlap more than twice, it might look a bit strange...
The object's Name
The object's local axes' directions
Then, the option, you asked for: "Wire" to show the Wireframe
and the last one, to let one object be always visible, Xray. (useful for multilayered stuff and so on. - If multiple objects have Xray enabled, you see them in the correct order, but in front of all objects, which don't have it enabled.