Desmos.com - Amazing free graphing calculator

TI-84 for Android | TI-84 for PC/Mac - Instructions

WolframAlpha.com - Calculator and equation solver that accepts a lot of natural language

Printable graph paper

SAT:

Official SAT Practice Test '12-'13 Youtube Playlist - Handwritten solutions and original pdf in description

ACT:

Official ACT Practice Test '12-'13 Youtube Playlist - Handwritten solutions and original pdf in description

GRE:

Official PowerPrep II software

Official Math Review

Video solutions for PowerPrep II and the Math Review

GMAT:

Official GMATprep v2 software - New format

Official GMATprep v1 software - New format

Official PowerPrep software - Old format 

Geometry:

Official Regents Geometry Youtube Playlist - Handwritten solutions and original pdf in description

jmap.org - PDF of all 456 past Geometry Regents questions sorted by topic

MathOpenRef.com - Interactive examples of definitions and animations of constructions (scroll down)

TTC Geometry Video Series - Geometry Lectures

Khanacademy Geometry - Lectures and exercises with hints

Jmap.org Videos for Pearson text - Poor video player doesn't allow rewinding but usually good short examples

Algebra I:

Official Regents Integrated Algebra Youtube Playlist - Handwritten solutions and original pdf in description

jmap.org - PDF of all 585 past Integrated Algebra Regents questions sorted by topic

Khanacademy Algebra - Algebra video series and some good exercises with hints

Algebra: In Simplest Terms - Algebra video series

Algebra II & Trigonometry + Precalculus:

jmap.org - PDF of all 273 past Algebra II & Trigonometry Regents questions sorted by topic

Khanacademy Algebra

Algebra: In Simplest Terms - Algebra video series

Calculus:

MIT - Calc I & II Lectures + Recitation

UMKC - Calc I Lectures + Lecture titles and links to sections

HippoCampus.org - AP Calculus AB & BC

coursera.org - Single Variable Calculus - Not to be taken as your 1st calculus course

Physics:

The Mechanical Universe - Physics I & II Video Series. Great animations and introduction to topics but a lack of examples means it has to be supplemented. Also a lot of history.

MrThomasPalmer.com Physics Lectures - Lectures and examples

Statistics:

Khanacademy Probability & Statistics

Elementary & Middle School:

The Singapore math textbooks are not free but are good at teaching through scaffolding examples. Thus, I stay stocked for all grades available.

Khanacademy Arithmetic & Prealgebra -Video series and some good exercises with hints

Sumdog.com - Fun math games site