I need to ask questions and get responses as quickly as possible. I know Stack Overflow is really very good, but I want to get another forum better suited for discussions with other programmers.
It's hard to get faster responses than you get them here, but if you look for raw C++ knowledge, have a look at comp.lang.c++
(you know, these old-fangled Usenet thingie, hard to use with a web browser). Be prepared for a somewhat harsher tone than you find here, though.
If you can live with answer taking longer, but being filtered better, look at comp.lang.c++.moderated
instead. If you feel like there's a defect in the C++ standard, ask at comp.standard.c++
. Both are moderated, which makes for a very good signal/noise ratio, but brings response times down to several hours at least (up to a day). Also, since everybody only sees everybody else's answers hours after they were posted, simple questions sometimes get flooded with at least half a dozen more or less equal answers.
I don't know not why you say Stack Overflow is very good yet are looking for another forum to discuss stuff with programmers, but still:
Another one you may wish to try is http://cboard.cprogramming.com/
They not only cover C, C++, and C# but also Windows API programming as well as other technologies.
The C++ channel on IRC right now has 558 people logged in, ready to answer your questions.
Stack Overflow is very good in case you need your answer in couple of minutes and you believe on collaboration. If you just want your answer then go with comp.lang.c++ but if you really want to discuss your problem then SO is better.
Stackoverflow is the fastest site around that I've found (by a LOT). If you feel you must search out other sites, see my updated list
The two "fastest/most hits" next to SO are
But codeguru and dreamincode are also great for (and slightly more specialized towards) C++ :D