"deniers" and "revisionists" are the two titles i'm familiar with. i'm not sure they are different, but i believe they are.
as someone already said, history is written by the winners. personally i do not deny the holocaust happened, but i do tend to doubt the numbers quoted and various other details i've found evidence which suggests the total number of Jews (discounting all the other people murdered) is closer to 1.5 million, not 6. a visit to the Red Cross website will confirm this, though this was not the only source.
i do know this: anyone that researches this subject and disagrees with significant parts of the "official story" is very likely to be labeled an anti-semitic and pounced upon by Nazi-like people from the JDL for doing little more than asking questions. i have read some of what these people have written, including their threats, and there is no doubt that some of these people act no differently than the Nazi's did.
here are some of the links i used in the very brief research i did:
http://judicial-inc.biz/Auschwitz.htm
http://www.geniebusters.org/915/04h_Cole.html
http://www.revisionists.com/
http://www.stormfront.org/truth_at_last/holocaust.htm
David Cole is a particularly interesting individual. he's a Jew who traveled to Germany and made a documentary about Auschwitz. it is said he came under harsh criticism by the JDL and may have had his life (or the lives of family members) threatened. he later recanted earlier statements he made regarding the holocaust.
i will also add: do NOT make the mistake of accepting anything at face value. do your homework and decide for yourself.