Carl's Pomerance "A tale of two sieves", available at
http://www.ams.org/notices/199612/pomerance.pdf
It makes a quick introduction to subexponential factoring algorithms via their development from Fermat's Algorithm and then compares the Quadratic Sieve with Her Majesty the (General) Number Field Sieve, in a thorough, appealing and very understanable manner.
