UVa

The Valladolid University Online Judge (UVa) Problemset
http://acm.uva.es/problemset

History
This site has been around for quite awhile, with over 4 million submissions as of November 26th, 2005.

Problems
Please use the Problem Template when adding new problems; see Help:Editing for a step-by-step guide.

felix-halim.net
An archive of helper utilities, such as a statistics comparer, a sorting of the easiest problems and separated ranklists for the countries.

Methods to Solve
Compilation of various methods to solve the problems. Has methods for about 35% of the problems.

ShyGypsy Labs
Various tools for UVa problems.