evildick

Here's some popular ones:

Boytaur fetish
http://www.boytaur.net/home.html

Amputee fetish
http://oddbeauty.com/open.html

Cast fetish
http://www.castfetish.com/main.html

Disability fetish
http://www.cripplexxx.com/all_galleries.htm

Diaper fetish
http://www.ibigbaby.net/ayanna/ayanna2.shtml

Conjoined twins fetish
http://www.conjoineddreams.com/

Pregnant smoking fetish
http://www.smokesigs.com/shs/babydoll/babydoll.htm

Drowning woman fetish
http://www.aquafan.com/

Breast cancer fetish
http://breastwriter.allbreast.com/

Hairy back fetish
http://hairyback.com/gallery/index.php3

If you don't market to all of those niches you might as well be throwing money away.