In order to obtain complete control over the "commercial" blackbox codes, it is imperative that users discuss the finer details of the code implementation (user functions) so as to maximize the benefits ..the code has to offer. As most of the readers know, CFD-online has the primary source for many of us. Given that, several other forums such as
Fluent University Forums:
can provide elaborate discussions on certain stuff that may be missing in CFD-online.
I, in fact, strongly recommend Fluent users to become a part of the Fluent University Forum community. Besides getting answers from fellow CFD users, sometimes the developers themselves post results to queries which just makes it perfect ;) - straight from the source. Search for other topics (anything in Fluent) and errors/bugs that you think exists within the code can be discussed here. In fact, this portal serves as a nice forum to let Fluent guys know your exact problems.
Website providing tips for CFD modeling (especially multiphase flows such those using VOF etc) are also very helpful
I came across this site where manuals for different softwares and discussions pertaining to their usage are available.