Valgrind, an open-source debugging and profiling toolsuite, is available from http://www.valgrind.org. Please visit that site if you want more information. We only use this SourceForge site for hosting our email lists.
Easy to use and works.
basically the only tool on the net to do what it does (well). Catch all you memory conditions, stack, allocations, uninitialized variables... Not entirely easy to use sometimes, but powerful and irreplacable.