If you'd like to see a great collection of striking stem cell images, look no further than the California Institute for Regenerative Medicine's Flickr photo stream. This image comes from the "Human embryonic stem cells" set and, according to the description, it shows:
Two colonies of human embryonic stem cells carrying the mutation causing Marfan syndrome. The line was derived from a donated IVF blastocyst determined by pre-implantation genetic diagnosis to have the mutation, which affects 1 in 5000 individuals. This line will allow researchers to study the underlying molecular mechanisms disrupted in Marfan syndrome with the goal of discovering new ways to treat people with the disease.
The image was made in the lab of Julie Baker, PhD, at the School of Medicine.