I have written one here: http://loup-vaillant.fr/tutorials/fast-scalarmult

It explains various constant time and variable times ways to do scalar multiplication (assuming constant time point addition), and clearly marks what is constant time (like combs) and what is variable time (like sliding windows).

One big missing part is modular multiplication, needed to perform constant time point addition. I explain some of it in my Poly1305 tutorial (search for "Cheating at modular arithmetic"): http://loup-vaillant.fr/tutorials/poly1305-design

There aren't enough tutorials and public domain code in the elliptic curve space in general (especially wrt NIST B and K curves).