Here are some links to useful sites with self-assessment tests and more:

Myers Briggs - various online tests from $39 and up

FRESS RESOURCES and TYPE DESCRIPTIONS

Adapted Myers Briggs Test by Humanmetrics - free adapted Myers Briggs test based on Jung Typology

53 Question adapted Myers Briggs Type Test by Similarminds  - 53 question adapted Myers Briggs test. The test starts asking for your gender and once you submit your answers, immediately gives you a result statement and links to read up more about your type.

The Personality Pages - The Personality Pages provide descriptions of the 16 types, typical careers for each type and even information about how to apply them to relationships and your personal growth.

Keirsey 16 Portraits - Keirsey describes the 16 personality types. Each 1-2 page portrait describes one of the personality types, observing them at work and at play, with family, friends, and colleagues, and emphasizing their unique strengths and talents.

Geocities MBI Introduction - Great and very simple introduction to MBI.

Personality Pathways test - Personality Pathways have a good description of the MBTI and offer another version of the test.