technoweenie

sentry

Painless encryption wrapper library

can_search

Build common named scopes automatically, and provide a simple way to merge them with a single #search call.

model_stubbing

Replacement for ActiveRecord fixtures using an extremely flexible ruby-based approach.

permalink_fu

ActiveRecord plugin for automatically converting fields to permalinks.

acts_as_versioned

ActiveRecord plugin for versioning your models.

masochism

ActiveRecord connection proxy for master/slave connections

attachment_fu

Treat an ActiveRecord model as a file attachment, storing its patch, size, content type, etc.