General Prohibitions

      Causing one's self to have sexual thoughts: Shabbat 140b; Niddah 13b
      Ex-communication for one who causes himself to have sexual thoughts: Niddah 13b
      One who causes himself to have sexual thoughts cannot enter into the inner area of Gd: Niddah 13b
      It is better to have one's stomach split open, than to descend to "the well of destruction": Niddah 13b
      The punishment for wasting semen: Niddah 13a
      Comparing the waste of seed to murder and idolatry: Niddah 13a
      Chopping off the hand of one who holds his member: Niddah 13b
      Adam creating demonic spirits with seed he accidentally wasted during his one hundred and thirty years of ex-communication: Eruvin 18b


Specific Acts

      Sleeping "Perakdan" [generally assumed to mean supine]: Berachot 13b; Niddah 14a
      Standing on a bed in which a couple usually sleeps: Shabbat 140b
      Touching one's genitalia to check for emission of [impure] seed or for [impure] genital discharge: Niddah 13a
      Holding one's member/genitalia while urinating: Niddah 13a-b, 16b, 43a
      Masturbation is like spilling blood: Niddah 13b
      Comparing masturbation to adultery: Niddah 13b
      Touching one's self to remove a thorn from one's groin area: Niddah 13b
      Wearing pants which are tight-fitting in the crotch: Niddah 13b
      Donkey and camel riding: Niddah 14a

Sources taken from Webshas