Mike,
 
You can use a double arm fiber optics light source to illuminate your sample
obliquely.  Bend the light pipes around so that they shine in roughly parallel
to the bench, from opposites sides if your sample is in a petri dish.  If
working with tissues in a droplet on a flat surface, you might try routing the
pipes in slightly above the sample but still shining on it from opposite sides.
 
A black surface beneath the petri dish sometimes helps.
 
Regards,
Glen