Some of these are (annnotated) slides from Colloquium Lectures, and some are just topics I've been playing with.
Continued Fractions, Continued
Counting with Groups
Slide Rules
A Tale of Two Sequences
Leonhard Euler, on His 300th Birthday
Proofs from the Other Book
Learning how to draw graphs in LATEX
Burnside's Lemma and Applications
Some Lemmas for the Fundamental Theorem of Algebra