The 3 main types of cells in epithelial tissue, classified by their shape include: columnar, cuboidal, and squamous. 

1. Squamous epithelial cellsare slightly rounded, and flat in shape, consisting of a small nucleus in the middle of the cell.  
2. Cuboidal epithelial cellsare cube-like in shape (have equal height, width, and depth), and consist of a spherical nucleus in the center. 
3. Columnar epithelial cellsare column-like in shape, and consist of an oval-shaped nucleus in the basal region.