How basic is "basic"?

For the "basic" material I like the book "Introduction to Smooth Manifolds" by John Lee very much. It's very friendly and very accessible and nicely explains the ideas. Spivak's "Comprehensive Introduction to Differential Geometry" is also very nice, especially the newer version with non-ugly typesetting. Warner's book "Foundations of Differentiable Manifolds and Lie Groups" is a bit more advanced and is quite dense compared to Lee and Spivak, but it is also worth looking at, after you become more comfortable with the basic material.