What are the best programming languages to learn for a future in Internet startup companies?

In addition to LAMP that Sean mentioned there is Ruby on Rails, Django, http://ASP.NET, and even WordPress, which can be considered a platform on its own. I am intentionally omitting Java (J2EE) because I feel its time has come and gone. I almost feel this way about http://ASP.NET too, but it still makes sense for many organizations. I recommend you become familiar with architectural patterns such as MVC, as opposed to specific implementations of these patterns. Also learn SQL, as most web apps are backed by some flavor of SQL database. Client-side JavaScript is very important to learn as well. Start with a basic JS tutorial, but quickly come up to speed on jQuery, AJAX, JSON, and related technologies. All the above suggestions will provide you with a foundation for success. I wish you the best of luck!

There are several options, but my programming language of choice is PHP. In my case, I develop on the Linux / Apache / Mysql / PHP (LAMP) platform. PHP is widely used and supported. There exists a substantial development community from which you can pull resources as needed. Most hosting companies provide PHP and Mysql for their Linux virtual hosting accounts, so you'll have many to choose from. There are additional scripting languages that play a supporting role in my business ventures. On the client, there is of course Javascript. On the server, I will sometimes rely on Perl (it has its strengths) and Bash (a simple scripting language built into a popular Linux command line "shell"). I'd be interested to hear of other language recommendations. Back when I first began web development consulting (1997), I developed dynamic web sites in ANSI-C :) It made for hellishly fast page generation performance, but hellishly slow application development!