Can anybody recommend fast and reliable open source codec for speech? Based on it's own good experience. Should be written in C/C++ and usable on Windows platform.

Thanks.

Speex pass all your requirements!

Thanks solaris, I'll give it a try.

Can you recommend the version?

Newest version, of course.

^ What he says!

That said, to be safe use the current stable version.
But if you want to test the latest features and are aware of the possible problems, check out the current unstable version!