Working fully functional 64 bit debugger with a GUI that is IDE independent?
 

Title says it. DDD seems to be dead, looking at the bug-list on their website and the fact that I can't get it to work even remotely. Nemiver sort of works but the memory-view feature seems to not be working and is also limited to 32 bit addresses.

I am working on Ubuntu 12.04 LTS (64bit). Please help me find a debugger.

Not really this big full featured debugger; however what about GDB? I use GDB in conjunction with gnuemacs and it is source level, graphical to some degree through that interface. GDB works with 32 & 64 bit sized architectures. It also works with a remote target if you use GDB coupled with GDBSERVER. I don't know what you mean by "IDE Independent" however command line GDB is absolutely IDE Independent.

I've never really played much with GDB through GNUEMACS because it's easy enough for me to run it command line; however I had open a test C file my hex-dump.c to dump out a binary/ascii file in hex so I ran the debugger and opened some frames to look at the stack (one level main only), watch a variable - string array, look at my locals vars, and inspect memory.

Seems serviceable. Here's a screenshot.

Use a command line debugger. GDB is probably the best free debugger for Linux.