Here I am collecting a list of proofs that I encounter (or write) and
particularly enjoy for one reason or another. Mostly for my own
reference, but someone else may enjoy them! Most are not very difficult,
but present ideas from an angle slightly different than is traditional.
I hope to eventually type up rigorous LaTeXtypeset proofs of each of
these and post them here, but that may have to wait a while...

The completelyvisual proof of the logsum rule. (Exercise from
Donald Knuth's The Art of Computer Programming)

A \cup C = B \cup C and A \cap C = B \cap C implies A = B. (From my
discrete mathematics course)

A special case of the Chinese Remainder Theorem, which can be
modeled by and proved from a patterned, subdivided rectangle.
(Used in a problem from Knuth's TAoCP)

The algebraic rule (a+b)^2 = a^2 + 2ab + b^2 visually with a
physical square diagram. (From my evolution and ecology Biology
course)

p^2 + pq = p for alleles in a HarveyWeinberg equilibrium
population. (Evolutionecology course)

Three different explanations for the formula n(n+1)/2 for
determining the number of possible genotypes given n alleles.
(Evolutionecology course)

Path independence of conservative vector fields, building off of
the famous Escher piece. (Vector analysis course, Hofstadter's
Godel, Escher, Bach)

Generalization of the Jacobian of higherdimensional spherical
coordinate systems. (Vector analysis course TA)

The Lame proof of the worstcase complexity of the Euclidean
algorithm, using the Fibonacci series. (Discrete mathematics
course)

"Godel for Goldilocks" by Prof. Gusfield.
Where to next?