For online, reaction-time based experiments I use Adobe Flash programs to collect data (ala Simcox & Fiez, 2013). So far, this has meant hosting the Flash program on a private server, exporting the data as an XML object to a PHP script that then converts it into a CSV file for download. My PHP scripts are an ActionScript 3 (AS3) version of the (very helpful) AS2 code developed by Jeff Galak for his “Flash for Behavioral Researchers” workshops.
I’ve explained the method in detail for anyone who wants to get started. Nota bene: Follow my advice at your own risk, and make sure to do your own homework.
[This post has been updated as of 9/13/2014, after several implementations of this method in actual studies.]