Differential Geometry: A First Course in Curves and Surfaces [pdf] 1 year ago
This is a nice textbook. We used it when I was an undergrad in Brazil and those were some of the most fun classes I've ever had. It gives you a ton of intuition and understanding for classical (extrinsic) differential geometry, and I feel that this experience was very helpful later in learning Riemannian geometry and General Relativity. It also helped a bit when I took an intro course to computer graphics. Solid stuff!