The famous reference Handbook of Mathematical Functions by Abramowitz and Stegun is on the web!
If you're stuck on a desert island with internet access:
If you're stuck on desert island with a laptop but have no internet access, you can get a very large electronic file:
http://www.lacim.uqam.ca/~plouffe (71 MB)
http://www.math.sfu.ca/~cbm/aands/dl/abramowitz_and_stegun.tar.gz (43 MB)