The Big Five Personality Test
A 60-item short form of the Big 5 using items from the International Personality Item Pool. To see the list of items selected from, click here. You can also review the item characteristics, including response frequencies and other descriptive statistics. Feedback based upon norms derived from John Johnson is provided. Distributions of scores from a sample of 50,000 subjects for each of the Big 5 domains can be found here. William Revelle, Northwestern University. Part of the Personality Project.

Also:
An online study of personality and social interaction.
Several personality tests from the University of Illinois Department of Psychology
A 46 item short form of the "Big 5" Personality Inventory using items from the International Personality Item Pool is available from Tom Buchanan at the University of Westminster. Feedback is provided.
A long form (300 items) and a shorter (120) item form of IPIP is available from John Johnson. Feedback is provided.
Yet another short form of the Big 5 is available as part of Frank Sulloway's studies of personality and birth order.
An online study of personality and performance from the Universisty of Minnesota (gone missing)
See also the list of online Social and Personality experiments maintained by Scott Plous at Wesleyan University.
Online research Projects (taken from the APS)
How to put studies on the web by Paul Kenyon, University of Plymouth

In addition to these, there are a number of websites that provide information of particular use to personality researchers:

IDANET Individual Differences and Assement Network is "a mailbase administered network for students, academic researchers and professionals involved in the definition, theory, and measurement of individual differences. The net members are drawn from the areas of experimental, clinical, and educational research, encompassing fields as diverse as psychophysiological assessment, psychometrics, personality theory and measurement, and cognitive ability. The range of specialisations encompassed within individual differences research provides for a rather wider content area than most other nets. However, that is why individual differences research remains so interesting."
The Guide to Social Psychology Laboratories maintained by Eliot Smith at Purdue includes a set of Cognitive-Social Reprints from a number of different researchers.
The Social Psychology Network maintained by Scott Plous at Wesleyan University is a very complete set of readings and links primarily for social psychologists. See particularly the list of research tools including search engines, lists of software and other reference works.
Neuropsychology Central offers links to resources for neuropsych assessment, brain imaging, medical and research laboratories dedicated to neuropsychological theory and practice.
A list of psychophysiological laboratories was maintained by the University of Southern California. (missing)
The Geneva Emotion Research Group has useful links and information about personality and emotion research.
Assessment & Evaluation on the Internet -- ERIC clearing house Internet resources of particular interest to the assessment community. (This is the revised version of a classic information source for educational and evaluation research.)
Statistical information is available from A Guide to Statistical Computing Resources on the Internet or Statistics on the Web
The Society for Computers in Psychology has an abbreviated page with some links to ongoing psychology experiments. In particular, look for the link to Ulf-Dietrich Reips "Standardds for Internet-Based Experimenting".
The R project, based upon the S and S+ stats packages, has developed an extremely powerful set of "packages" that operate within one program. Although described as merely "an effective data handling and storage facility [with] a suite of opeators for calculations on arrays, in particular, matrices" R is, in fact, a very useful interactive package for data analysis. When compared to most other stats packages used by psychologists, R has at least three compelling advantages: it is free, it runs on multiple platforms (e.g., Windows, Unix, Linux, and Mac OS X and Classic), and combines many of the most useful statistical programs into one quasi integrated program. (R is free software as part of the GNU Project. That is, users are free to use, modify, and distribute the program, within the limits of the GNU non-license). The program itself and detailed installation instructions for Linux, Unix, Windows, and Macs are available through CRAN.
Tutorials for using R in Psychology have been written by Jonathan Baron and Yuelin Li to use R in the Psychology lab. Another is written for undergraduates and graduate students at Northestern and is available as part of the personality project.
Information about how to prepare effective visual presentations is available from Kansas State University.
Personal Construct Psychology and the Personal Construct Research Group offer applications of George Kelly's Repetory Grid Test technique whic may be applied to organize knowledge structures about people as well as situations.

The Personality Project

Online Personality Research Projects