essentialmedgen.com

Websites for computer-aided syndrome diagnosis

Links to powerful commercial and freely-available resources for this purposeare provided here.

OMIM

Online Mendelian Inheritance in Man.

Phenomizer

Freely available but not expert-curated.

This resource, although it may not be free, is expert-curated, designed for professionals and provides many carefully selected photographs.
Possum database
Another database that, although requiring purchase, is useful for the diagnosis of dysmorphic cases.
Orphanet

Freely available. It contains a new facility for searching by clinical sign.

For more details and for a user's guide on how to make the most efficient use of these databases, see Part 3 of Essential Medical Genetics 6th Edition