Genetic Resources:

Gene reviews.org:  Technical descriptions of a large variety of genetic diseases.  Sources are easily cited, but the highly technical writing can be confusing.
http://www.genetests.org/servlet/access?id=8888891&key=p3p4U09QBGct7&fcn=y&fw=1zlq&filename=/reviewsearch/searchdz.html

Genes and Disease website:
Disorders can be searched by chromosome.  Descriptions of the disorders are fairly brief.
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd.TOC&depth=2

Your Genes, Your Health:
A relatively small number of disorders are covered, but the ones that are listed are covered in detail.  Each disease has several slides to click on for different information.
http://www.ygyh.org/

Mayo Clinic.com:
Searchable database overviews a tremendous amount of disorders.  I suggest looking at the resources used because the descriptions are fairly general.
http://www.mayoclinic.com/

Medlineplus.com: 
Same type of website as Mayo clinic.  For the most information, I suggest following their resources.
http://medlineplus.gov/

Genetic Disorder information on the Web:
Genetic disease links page with many useful resources.
http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/diseaseindex.shtml