Moments
zedstatistics - What are "moments" in statistics? An intuitive video!: Explains moments, mean, variance, skewness and kurtosis.
ANOVA
Edward Roauldes: Analysis of Variance, Tukey's HSD: Around the 5 minute mark he explains why it's a dumb idea to used paired t-tests instead of ANOVA with Tukey's HSD.
Limits
Epsilon-Delta definition of a limit: Simple explanation.
Calculus of variation and mechanics
Andrew Dotson - Converting From Lagrangian to Hamiltonian Like An ABSOLUTE NORMIE: This made sense to me (since I'm not really interested in applications of calculus to physics...).