How can I create helpers in Laravel and where should I put them? I was thinking on something like codeigniter's approach: a helpers.php file and some helper functions in there where I can call as needed.
There is not much about the subject in the documentation.
I really depends on what you're doing, but in Laravel 3 your goal should be to extract as many reusable portions of code into bundles. Take a look at the existing bundles and you might find something which will suit your needs built already (or at least good examples).
For "helpers" your still best off creating classes and defining the helper functions as static methods, this is clean and typically easy to follow.
If you don't want to create a bundle for the helpers, then you can also place them within the application/models folder, again wrapped in a class.
Here is a thread from the forum which shows some examples of "helper" type classes.