Favorite questions (that I did not answer but I find fascinating):
Proving the sum of a product is equal to pi
Double integral of a Gamma Function
An interesting summation
An interesting number theory answer
The convergence of a Zeta function product series
Favorite questions that I have asked or answered:
Cauchy-Euler Equidimensional DE $x^3y'''\left(x\right)+3x^2y''\left(x\right)+5xy'\left(x\right)-5y\left(x\right)=0$ http://math.stackexchange.com/a/1213835/167604