Here's a list of some project with great PCB artwork:

Pure art boards:

Full Panel PCB Painting

https://hackaday.io/page/3353-full-panel-pcb-painting-fabricated

http://blog.oshpark.com/2017/06/26/pcb-artwork-in-2017/

Hand-drawn PCB Artwork

http://blog.oshpark.com/2017/04/06/pcb-paintings/

Making Braille Signs out of PCBs

https://blog.oshpark.com/2017/11/02/making-braille-signs-out-of-pcbs/

PCB lapel pin

http://blog.oshpark.com/2017/07/05/building-a-pcb-lapel/

Full panel PCB sign by Andrew Sowa

https://www.instagram.com/p/BcGrEupBJQi/

Lumen Electronic Jewelry

http://blog.oshpark.com/2016/10/31/lumen-electronic-jewelry/

Creating the Benchoff Nickel

http://blog.oshpark.com/2017/03/30/creating-the-benchoff-nickel/

PCB Paintings Facebook group

https://www.facebook.com/pcbpaintings/

PCB Painting Art Nouveau

http://blog.oshpark.com/2017/02/12/pcb-painting-art-nouveau/

Convert Inkscape SVG drawings to KiCad footprints

http://blog.oshpark.com/2017/01/08/convert-inkscape-svg-drawings-to-kicad-footprints/

Functional boards with awesome art/layouts:

OSHWi Octopus Badge by Gustavo Reynaga

http://blog.oshpark.com/2017/12/24/oshwi-octopus-badge-by-gustavo-reynaga/

Trammell Hudson PCB art soldering badge

https://trmm.net/PCB_art

https://twitter.com/oshpark/status/885169000619159553/photo/1

Minifigure Atmel SAMD21 Board

http://blog.oshpark.com/2016/11/09/minifigure-atmel-samd21-board/

https://oshpark.com/shared_projects/QveMnbke

Cyborg Ring by @zakqwy  of neurotinker

http://blog.oshpark.com/2018/02/09/cyborg-ring/

Glowbugs by @JasMoH and reverse mount LEDs

https://hackaday.io/project/28155-silly-pcb-designs/log/71997-glowbugs

OSH Park PCB Crown

https://tekdemo.github.io/pcb-crown/

https://tekdemo.github.io/pcb-crown/images/2014-05-18%2019.55.57.jpg

http://blog.oshpark.com/2016/07/23/lessons-in-3d-circuits/

PCB Art With 4 Layer Boards

https://tekdemo.github.io/2014/09/18/PCB-art-with-4-layer-boards.html

https://tekdemo.github.io/images/no-know-coin//2014-07-01%2022.05.31.jpg

Brain board for Sarah Petkus' Noodle robot

https://pbs.twimg.com/media/CRjjlwWUAAEAKpD.jpg:large http://blog.oshpark.com/2017/04/30/robotic-arts-noodle-is-gettin-bean-feet/

https://roboticarts.wordpress.com/2015/10/24/the-walking-noodle/

Heart-shaped Flashlight PCB

http://blog.oshpark.com/2017/03/28/heart-shaped-flashlight-pcb/

Snowbot

http://blog.oshpark.com/2017/02/21/snowbot/

Trixel Interactive LED Kit

http://blog.oshpark.com/2017/04/04/trixel-interactive-led-kit/

4CHord MIDI

http://blog.oshpark.com/2017/07/27/4chord-midi/

https://twitter.com/oshpark/status/913954089461063680?s=19