Another question asks why Spirit and Opportunity weren't launched together. My gut response was that multiple-payload launches were less common then than they are today, but I don't actually know if that's true.
What was the first single launch to put two or more independent payloads into Earth orbit?
What was the first time, if ever, that a single launcher put two independent spacecraft on trajectories leaving Earth's sphere of influence?
Not included: multiple-warhead military applications, or balloons deployed from Mercury spacecraft or Gemini's "rendezvous evaluation pod"; the payloads have to go into different orbits, or at least phased substantially in the same orbit.