Patrick Woodroffe
Official Site
2nd Gallery
The Snake Tree of Lema

Royo and Altarriba - Hybris
1 - 2 - 3 - 4 - 5 - 6 - 7 - 8

Jacques Clavreul
One more Lovecraft gallery I forgot to mention. Jacques has made some great fantastic architectural illustrations as well.

Leonora Carrington
I've posted about Carrington before but hadn't been able to find a good online gallery representing her work until recently. Most of her strongest work is on display here.