I have a program in which I've lost the C++ source code. Are there any good C++ decompilers out there?
I've already ran across Boomerang.
You can use IDA Pro by Hex-Rays. You will usually not get good C++ out of a binary unless you compiled in debugging information. Prepare to spend a lot of manual labor reversing the code.
If you didn't strip the binaries there is some hope as IDA Pro can produce C-alike code for you to work with. Usually it is very rough though, at least when I used it a couple of years ago.