Depending on your definitions, the contenders seem to be the US Space Shuttle, Buran, Apollo 17, or Skylab.
Apollo 17 + S-IVB translunar 143 t?
STS, maximum payload 115 t
Discovery STS-82 106 t
STS, no payload 90 t
Buran + payload 87 t?
Polyus 80 t?
Skylab 77 t
Buran, no payload 75 t?
Apollo 17 CSM/LM 47 t
Skylab was 77 tons, launched as a single payload on a Saturn V (in fact, the station was converted from a Saturn V third stage).
The Apollo CM/LM stack was under 45 tons, but for the lunar missions, in low Earth orbit it remained attached to the Saturn's S-IVB third stage, which provided the fuel and engine for the translunar injection burn. The S-IVB burned a small amount of its fuel to get into LEO, but that left the combined translunar spacecraft massing over 115 tons.
The Apollos grew slightly in weight over the course of the program, as the launcher engines were uprated, confidence in safety margins improved, and more equipment was brought along. Apollo 16 and 17 were the heaviest, with 16 weighing a little more at launch, and 17 a little more in LEO (having used a bit less fuel getting there). Adding up the launch weights of components listed in Apollo By The Numbers, then subtracting the LES and the fuel used in the initial third-stage burn suggests an orbital mass over 140 tons.
The Space Shuttle orbiter masses over 68 tons dry, and carries a payload of up to 25 tons; its maximum takeoff weight ranged as high as 115 tons. I found a source giving Discovery's orbital mass as 106 tons for the STS-82 mission. As with the S-IVB, the orbiter is ambiguously part launcher and part payload.
The Soviet Energia booster was second to the Saturn V for payload-to-LEO, with approxmately 100-ton capability. It flew twice: once with the Polyus payload described in Puffin's answer, once with the Buran spaceplane. Astronautix manages to give two very different weight figures for Buran on a single page. It's either a little lighter or a little heavier than STS.