Fast, Minimum Storage Ray-Triangle Intersection
T Möller and B Trumbore
Paul Bourke's homepage
Lot's of articles useful for computer graphics, e.g. distance algorithms between different geometric forms.
Intersection of a Line and a Sphere (or circle)
Nov, 1992 - Paul Bourke
This is an open source math and geometry library for C++. Besides having a lot of useful classes and functions, the site also has a lot of links to other resources on related subjects.
This site holds lots of interestering documents describing algorithms, mostly on geometrical computation, but also other more generic applications. The site is also home to the programming library Wild Magic, which is available under the Boost license.