What is the Best Memory Debugger?

laci asks: "I'm sure many of you have used memory debuggers in the past. I have used Purify before, but now I need a memory debugger for Linux and/or AIX. My main concern is that the application I'm working on does a HUGE number of memory allocations (100s of millions). A constant factor slowdown is acceptable (even if it's a factor of 10), but the debugger should not slow down to a crawl. Also, I'd like to know which memory debuggers work on both platforms (I know of insure++ only)."