Here's an odd space-filler -- a truncated tetrahedron. But not the truncated tetrahedron, this basically has edge lengths of 1 and 2, instead of all 1.

tetfiller[t_,{a_,b_,c_}]:= With[{tt={{4,2,2},{2,4,2},{2,2,4},{-2,4,-2},{-4,2,-2},{-2,2,-4},{-2,-2,4},{-4,-2,2},{-2,-4,2},{2,-2,-4},{2,-4,-2},{4,-2,-2}},
tt2={{-2,-6,0},{0,-8,0},{0,-6,-2},{4,-8,4},{6,-6,4},{4,-6,6},{4,-2,-2},{6,-2,0},{4,0,0},{0,-2,6},{0,0,4},{-2,-2,4}},
tf = {{1,2,3},{4,5,6},{7,8,9},{10,11,12},{2,3,7,8,5,4},{5,6,10,11,9,8},{1,2,4,6,10,12},{3,7,9,11,12,1}}},
Polygon[({tt,tt2}[[t]]+Table[a{6,-2,-4}+ b {-2,-6,4}+c{-6,2,-4},{12}])[[#]]]&/@tf];

And here's what it looks like.

  Graphics3D[{
  {Opacity[.5], Red, tetfiller[2, #] & /@ Tuples[{0, 1}, {3}]},
  {Opacity[.5], tetfiller[1, #] & /@ Tuples[{0, 1}, {3}]}},
 Boxed -> False, ImageSize -> 600, SphericalRegion -> True]

There are five space-filling tetrahedra, and a few classic space-filling polyhedra. I'd like to expand that last demo with a lot more space-filling convex polyhedra. Anyone have handy code for adding more?