This is a classic question which I get to answer a lot. N00bs know the answer, but somebody outside the IT-business might ask something like that. This is also quite a popular question among young people trying to figure out if programming would be for them.
Anyway, here 5 Programming Languages Everyone Should Know from two people who actually have created some of the most popular languages currently used.
Nobody should call themselves a professional if they knew only one language. - Bjarne Stroustrup
Again, seeing C++ in his list is not a big surprise, he was one of the authors of the language in the 80s. The funny thing is that he mentions 6 languages.
This two year old interview keeps popping up. In this video http://youtu.be/Aa55RKWZxxI mr. Linux mentions one programming language not to use.
The again, this person is well known from his more than colorful opinions about various issues. But anyway his work on Linux kernel and Git version management are well known, he is a fan of C.
Being a blog-author I have to express an opinion of my own. To solely copy/paste opinions of three very skilled persons is too much of a cheap thing. So, here goes:
Pretty much all languages created after 1970 owe something to C, it is imperative to know this.
When doing any kind of web-stuff, this is the only language being used in 100% of the cases. All browsers run this and it is the de-facto client-side language today.
Very versatile compiled language by Microsoft, has lot of influence from C, C++, Java, PHP, Perl, etc. the list goes on. It is mainly used with .Net to create server-side stuff.
In addition to learning programming languages, I encourage everybody to learn also following widely popular frameworks:
My reasoning between this is that if you understand how they work, you're pretty well covered and also going to Python/Django or Ruby on Rails is much easier task. I know that these are web-frameworks and people program a lot other stuff than web, but sticking to the topic of what languages to learn, these are the first ones to try. There are so many other frameworks, especially in PHP-land, but they don't have such an essential position as the framework made by people who created the PHP-language. In Microsoftland there are no other significiant frameworks to learn. Anyway, both are properly documented and lot of information can be found of them.