A malloc(3) debugger library written by Paul Nettle who writes for 
http://www.flipcode.com. Quite useful and featureful, works well for both C and C++. A download link can be found here.
I used MMGR in a medium sized C++ project; it was around 10,000 lines not including external libraries (of which there were many). It found a all the memory leaks which were leading to quite a memory hungry program. This library might be an option for platforms Valgrind is not available on -- SamJansen
