Enter a sample ratio in one of the three input boxes, and WebMath will explain a bit about it.
This all-Flash site explains ratios using interactive manipulatives.
This seven-page lesson from Purple Math has lots of word problems where the work is shown, and the answer explained.
Algebra Help's four-page introduction to proportion, means and extremes concludes with a twenty-question worksheet that includes both a manual answer sheet and a step-by-step solution to each problem.
Website reviews for ratio and proportion.