In a human, what non-germline cells have the highest/lowest mass?
Large cells: adipocytes, the cells that store fat are possible the largest in humans, because after puberty they rarely divide and just enlarge if a person gains weight. A typical adipocyte is about 0.1mm in diameter, but may be a lot larger. Another good candidate is a megakaryocyte, which is a gigantic (up to 0.1mm), cell with multiple copies of its genome producing blood platelets. Depending on your definition of a single cell, also myocytes may be considered large cells, because during development several cells fuse to form one muscular fibre. Additionally, myocytes gain weight if a person excersises and strengthens muscles.

Small cells are more common, and it is difficult to point to some consistently smallest cells. The smallest kind-of-cells are definately platelets and erythrocytes (red blood cells - they are anucleated, thus may not be considered "real" cells). Generally, the part that determines the minimum size of the cell is the nucleus, so any cells, that are more-or-less metabolically inactive may be just a tiny bit larger than the size of their nucleuses. These may be for example polar cells, the tiny cells, that carry the excess of genome during meiosis in women and die soon afterwards.

If you are interested in all kinds of strange cells inside yourself, you might start by browsing this beautiful, though longish list.