Math

• Eric Weisstein's on-line math encyclopedia
• The Erdös Number Project
• Mathematical Constants
• Great Internet Mersenne Prime Search (contains a list of divers distributed projects)
• Inverse Symbolic Calculator
• The Prime Pages
• Sci.Math FAQ
• Comp.Theory FAQ
• Number Theory Web
• Elliptic curves theory
• Math problems worth 1 million $ each
  

Crypto

• Adam Back's crypto hacking and politics page
• FactorWorld
• Peter Gutmann's page, X509 and Microsoft hacking and much more.
• Stefan Brands' private credentials
• Helger's crypto pointers,  most cited cryptographers.
• List of Cryptographers
• Camenish's list
• Lipmaa's list
  
• McCurley's list
• Rivest's list
• SIRENE's list
  
• Wagner's list