Serjan Burlak has created some very cool renders using Arnold and Houdini.

Awesome work by Jacques Defontaine using Arnold.

Some incredible shading work by Max Tarpini using Arnold.

Below are some comparison test renders of the diffusion SSS (default) with the new randomwalk SSS.

Diffusion

Randomwalk

Diffusion

Randomwalk

Diffusion

Randomwalk

Diffusion

Randomwalk

Diffusion

Randomwalk

Monica from Academic Phoenix has a great series of videos aimed at Maya for Arnold (beginners).