Mpatrol

A great, open source, memory debugging tool. It can also be used even though the original program might not have been compiled with the library.

Has very good support for various systems like (various)linux, tru64, windows etc.

Have been able to compile the same for Tru64 on Alpha machine. Though, still not been able to get it working properly but seems to be pretty good. Can give Insure++ a run for money.