Try marijuana. A good dose is guaranteed to make you forget what the fuck your name is, or how to breathe/blink, etc. I know I've done all three.
I replaced X with cocaine for a while. Then I got bored with uppers and turned to Opiates and Marijuana. LSD is awesome but not something you can really do very often, not for me anyways. Whoever suggested PCP is insane. I don't see how people even enjoy a PCP trip. I got some xtc with that shit in it once and it was the most horrendous experience ever. I swear I saw death that night... I was going to commit suicide to make it all stop. Thank god someone was there to calm my ass down... or atleast keep any weapons away from me.