LSD probably did not assist Francis Crick in discovering the double helix. Although LSD was available in 1953, it wasn't widely known or used until the 60s, and there's no evidence Crick would have had access to it (see the excerpt from Matt Ridley's book at http://skeptics.stackexchange.com/questions/6835/was-francis...). This story seems to have originated with a Mail article published after Crick's death (http://www.miqel.com/entheogens/francis_crick_dna_lsd.html), and AFAIK has never been verified. While other evidence suggests that Crick experimented with LSD later in his life, he probably did not discover the double helix under its influence.

OTOH, Kary Mullis explicitly attributes PCR to his LSD use. I'd ordinarily believe the primary source over uninformed speculation, but Mullis is also an AIDS and climate change denialist who claims he once spoke to a glowing green raccoon, so he is probably not the most reliable source either.