Altough gdb is not a real low-level debugger, it has some quite interesting low-level functionality.

(gdb) dump binary memory dump.raw 0x00800000 0x01000000

Dumps the memory of the currently debugged application into a file 'dump.raw' from address 0x00800000 to address 0x01000000.

Now, this file can be searched, processed or even modified using external tools. If desired, using the command restore it can be loaded back into the memory.

Interesting regions to dump and inspect can be found using tools like vmmap (on MacOS X). You will be probably most interested in MALLOC_* regions.