These exercises are all useful to help you understand yourself better and therefore what kind of careers you might want to follow.
Seligman Character Strengths
You need to register before you can use it (it's free). The questionnaire 'VIA Survey of Character Strengths' asks a number of questions and comes out with a list of strengths in priority order. This can be helpful in understanding what your preferences are.
Prospects planner /What jobs would suit me - on Prospect from the UK Graduate Careers Service. You need to register before you can use it (it's free). Fill in two short questionnaires and it will suggest a number of potential careers. Click on any of the suggestions for more information. This is aimed at UK university graduates, but there is no restriction on joining.
Self-Directed Search - Holland Types
This is a web-based process which produces a three-way characteristics profile based on John Holland’s six types: Realistic, Investigative, Artistic, Social, Enterprising, Conventional (RIASEC). Your results might be, for example, ASE – meaning primarily artistic, secondly social and thirdly enterprising. Once your profile is created, the website lists dozens of career suggestions for each profile. Look at the suggested careers and pick five or more that really catch your imagination. (There is a charge of $9.95 to take the test and see the list of suggested careers.)
A respected psychometric tool. This link is to a free version which gives career suggestions.
Myers Briggs Type Indicator (MBTI) - Personality Page
If you already know your Myers Briggs type, this site lists potential careers for the different personality types
Adapted from John Lees' excellent book How to Get a Job You'll Love
A USA site which lists a huge number of jobs with descriptions of what people do on the job. Worth browsing if you are looking for ideas. Includes non-graduate roles, so broader than Prospect.
Matching Passions to Careers
Lists potential careers to match to your passions