I don't have such a list, however I also think -but I just think this, it can always be different of course - that there doesn't exist such a list. There are thousands of programming forums out there, and of course there are some bigger forums, but it is impossible to index all forums to compare which belong to the 100 biggest ... but that is just what I think of course
If you are interested in Microsoft Visual FoxPro, you can try the Foxite. You can start forums and queries then other Foxiter will help you answer your question.
Programming is a very generic word... The list is different for interview programming, debugging, Microsoft concepts etc. And each one will prefer a different list in a completely different priority. Also you can never track 100 forums at one go. Check whether you can write the names of 100 sites (any site) that you know of? You cant cross 20 most probably
Big Boards tracks around sixty programming forums but there are many good forums missing from their lists. Big Boards - Top Programming Forums