Ibexfarm

Ibexfarm is a platform and hosting service to run questionnaire studies on the web. 
It can be used to run selfpaced reading, acceptability judgment studies and cloze tasks. In order to use it, you have to sign up on the website (free of charge) and set up the experiment by changing a collection of javascript files. Although there is no graphical user interface and the way it is implemented might not be intuitive for everybody, it is possible to use it without knowing javascript.
Ibex has build-in support for latin square designs and can be adapted to complex randomisation procedures.
Within em4, we have used Ibexfarm for an acceptability judgment study already and are able to provide assistance easily.
If you would like to see what an ibex study looks like, you can try it out here. The source file for this experiment can be found below.
In addition, you will find a set of slides (by Grégoire Winterstein) explaining the basic concepts and how to use it below, if you are logged-in.