I'd recommend learning something like Python over Lua as it is more widespread and is used in a lot more areas, but that's up to you.
Python can and is used for web development, though if that's what you're interested in then you might find PHP easier to get into.
Fortran is an interesting choice and I understand your reasoning, however I wouldn't put too much time into that right now (up to you, however, just do what you enjoy).
Basically, there are tonnes of choices each with their individual merits. Pick something with a decent community which you enjoy. Python, Perl, PHP, C, C++, Lua, Java, Javascript.. they all suit that perfectly. If you really can't make up your mind, toss a coin and read up on that language for half an hour and if you like it, keep learning :-)
Another thing to add: it's not just about the language. Once you've learnt a language, you need to learn the commonly used libraries/modules. How to decode XML/JSON, how to talk to a database, socket programming, etc, etc. You might find it better to concentrate on those in a language you already know. It's better to be an expert at one language than mediocre at a dozen.
Also, check this out: http://learnpythonthehardway.org/book/advice.html Just found it and it's sound advice.