Quantum EntanglementFour 2x2x2s arranged in tetrahedral shape. Every side's rotation is linked to the rotation of another cube.
Radio 3 OctahedronA Radiolarian 3 (a face turning icosahedron) redesigned to have the shape of an octahedron.
Raptor BallA spherical version of the Proportional-Oh-Cube but from a different designer.
RaskewbThe Mental Box after a 180° turn reshaped into a cube.
RCP CentroidA 3x3x3 in the shape of four intersecting cylinders.
Reuleaux TobleroidA five layered triangualr prism roughly in the shape of a bar of the famous swiss chocolate.