A large collection of useful algorithms.
The home page can be found at http://www.cs.sunysb.edu/~algorith/index.html
Sean Eron Anderson's page on [Bit Twiddling Hacks] contains several useful algorithms for manipulating bit fields.
Useful information on binary space partition trees.
The home page can be found at http://www.faqs.org/faqs/graphics/bsptree-faq/
A collection of useful [C snippets] by Glenn Rhoad.
[Amit's Game Programming Information] constains many game-related algorithms: shortest-path, A*, tile-based graphics, and AI programming.
A R-Tree is an index structure for point and spatial data at the same time.
The home page can be found at http://www.cs.cuhk.hk/~drsam/methods.html
Information and/or specifications on popular graphical file formats.
The home page can be found at http://www.dcs.ed.ac.uk/home/mxr/gfx/2d-lo.html
Splay-trees, a form of self-adjusting binary search tree an implementation of the pending-event set, the central abstraction underlying the sequential discrete event simulation algorithm.
The home page can be found at http://www.cs.uiowa.edu/~jones/event/.
The algorithms for balancing splay-trees can be adapted to data compression.
The home page can be found at http://www.cs.uiowa.edu/~jones/compress/.
Bob Stout's collection of C and C++ algorithms
The home page can be found at http://www.snippets.org.
MAGIC is an acronym for My Alternate Graphics and Image Code. MAGIC is intended to provide free source code for solving problems that commonly arise in computer graphics, image analysis, and numerical methods.
The home page can be found at http://www.magic-software.com/.
Sick of hearing people name off algorithms that you should use, yet you have no clue what they are, much less how to implement them? Sick of people who won't take the time to explain algorithms and instead reference you to a book that you can't afford?
The home page can be found at http://www.reocities.com/ResearchTriangle/Lab/1767/pol.html. If it moves the home page can be found at http://www.reocities.com/ResearchTriangle/Lab/1767.
...For many programming problems there are several simple and elegant algorithms that have been invented, but some of them are better than other in practical situations. These algorithms undergone a tremendous amount of polishing and peer reviews and usually you can be confident in their correctness and efficiency.