Very good Flash-based quizzes here on "choosing appropriate topic sentences," "writing topic sentences," and "identifying sentences that affect unity."  Lots of other exercises on other aspects of paragraphing as well.

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A well organized lesson that, like this lesson, begins with a pretest and a statement objectives.  The lesson is organized into chapters: audience, setting your purpose, making the point, adding supporting detail, creating unity, and creating coherence. Good coverage of paragraph skills.  From the Minnesota Literacy Council and faculty from the U. Minnesota system.

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A fun page with several visual representations of paragraph structure.  No text-based lesson here, but the graphics are useful for visual learners.  Oriented toward kids, but still relevant to adults.

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Excellent explanation from The Elements of Style by William Strunk about creating unified paragraphs.  Excellent examples and tips for stronger writing.  The language is a bit difficult at time for modern audiences, but the text is worth reading.

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