Where to find help about life in Berlin?

I try to answer as many questions as I can with this website, but there are still many stones left unturned and many questions left unanswered. Here is how you can find help for the topics I have not yet addressed.

Ask the English-speaking community

You can leverage the support of the following communities and its members.

Toytown Germany - Forum. Less active than before.
Free Advice Berlin - Facebook group
Berlin EXPATS - Facebook group
Berlin4Beginners - Facebook group
/r/berlin - the main subreddit for Berlin. Make sure you read the rules before posting.
/r/germany - the English-speaking subreddit for Germany. They also have a lot of information and a large community that can answer your questions.
Quora - a general Q&A website
Expatriates StackExchange - Q&A website for expatriates

Ask the German-speaking community

If you can speak German, the following communities can also help you

Gutefrage - a popular German equivalent to Quora and Yahoo! Answers
/r/de - the main German-speaking subreddit for Germany. It's the largest German-speaking community on reddit
/r/FragReddit - a much smaller subreddit where you can ask questions in German
Jeder hilft jedem - the largest German-speaking Facebook advice group for Berlin. You must first request access by confirming that you have read the group's rules

Ask a professional

We have compiled a few lists of English-speaking professionals to help you find legal, financial and medical assistance in Berlin.

Visa issues

"Working and Living in Germany" hotline: an official hotline that helps people settle in Germany. They speak English.
List of English-speaking relocation consultants
List of English-speaking lawyers in Berlin
The "Working and Living in Germany" hotline, a free, official hotline that helps people settle in Germany. They speak English.

Medical issues

Financial and legal issues

List of English-speaking tax advisors in Berlin
List of English-speaking lawyers in Berlin
Berlin Chamber of Commerce (IHK) - Offers help in English by phone, by email and in person

Apartment issues

Your tenants' association (Mieterverein) offers legal advice. You must be a member to use their services. Being a member is not expensive: the Berliner Mieterverein charges 9€ per month¹. The Berliner Mieterverein and Mieterschutzbund Berlin are the two biggest associations in Berlin.
Conny has a legal hotline for tenants. They have lawyers that can answer your questions.
A lawyer. Use my list of English-speaking lawyers. If you have legal insurance (Rechtsschutzversicherung), you can get their advice for free. If you don't have legal insurance, their help is very expensive.