The current hottest peppers are the chocolate bhutlah and the Carolina reaper. I believe the reaper was the Guinness record's holder in 2013; I think the bhutlah has been bred to the F5 or F6 generations, so it should be stable enough to win the record this year or next. The world record is not necessarily the best guide to which is the hottest, because different capsaicinoids produce different levels of heat, but the records are for capsaicin only. Here is a list of the hottest pods currently available and where to buy seeds (and sometimes cuttings).
A friend of mine from zoklet had a vial of 99.8% capsaicin powder out when I visited him one time. That shit is like weapons grade hot, it was 14,250,000 SHU (pure capsaicin is 16 million SHU).