Perhaps as an algebraic geometer, you might read his paper:On the (co-)homology of commutative rings , in Proc. Symp. on Categorical Algebra , (1970), 65–87, American Math. Soc.
This is fairly short and yet is one of the key papers in the area. It introduces ideas of homotopical algebra, which have been crucial in algebraic topology and algebraic geometry, yet the paper does not need a whole load of prior knowledge. The lecture notes on homotopical algebra and the paper on rational homotopy theory are beautiful in their use of techniques from adjacent areas to solve hard general problems and follow on from that initial work.
The algebraic K-theory papers are another thread, but these have been mentioned above.