More and more researchers are using the web to gather data for serious research, but they need your help as participants. As a proponent, I like to do my part and share the calls for participation that I know about. If you know of any others, I'm happy to add:
MPI -- The Max Planck Institute for Psycholinguistics: Investigates how people use language.
Cue-word memories -- Clare Rathbone, University of Reading: The study is specifically interested in the way people remember events from their lives. You will be asked to recall 16 memories and then rate them for details, such as vividness and how often you have thought about the memories before. You will also be asked to fill in two short questionnaires. Please note, this questionnaire is for people over the age of 40 only - please do not take part if you are aged 39 or younger.
Phrase Detectives -- University of Essex: Lovers of literature, grammar and language, this is the place where you can work together to improve future generations of technology. By indicating relationships between words and phrases you will help to create a resource that is rich in linguistic information.
Games With Words -- Joshua Hartshorne, Harvard University: Test your language sense! Play a game while participating in cutting-edge research. How good is your language sense?
Color Naming -- Dimitris Mylonas, London College of Communication: This is a multi-lingual colour naming experiment. It is part of research on colour naming and colour categorisation within different cultures, and aims to improve the inter-cultural colour dialogue. By taking part you are helping us to develop an online colour naming model which will be based on the "natural" language provided from your responses.
CogLab 2.0 -- The Cognitive Psychology Online Laboratory: Aggregated set of many online research projects.