I just put together a word cloud based on all the modules from this site. The cloud shows the top 150 words used by Drupal developers to describe their modules.
See more details, and a bigger picture, over on Blamcast.
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CAPTCHA
"Great module. Easy to configure. If you're having problems with spam get Captcha. I'd also recommend..."
BUEditor
"A newbie to Drupal, I was looking for a way how to implement my own CSS into an editor. Before Drupal..."
Node Access Control
"The "per node" access control the core lacks. Initially I'm little confused about "Permission name" creation..."