Corresponding Entity References

"CER keeps reference fields in sync. If you have two entities that refer to each other using Entity Reference (or some other kind of reference field), it saves you the trouble of double-editing your entities in order to have them point at each other. If entity Alice references entity Bob, CER will make Bob reference Alice, and keep the references up-to-date when either entity is updated or deleted."

Smart Trim

Smart Trim implements a new field formatter for textfields (text, text_long, and text_with_summary, if you want to get technical) that improves upon the "Summary or Trimmed" formatter built into Drupal 7

Video Filter

Lets you use tokens to embed video and have the ability to add a button to the WYSIWYG for easily adding a video (for those to0 lazy to type).

Flag

Flag is the ultimate bookmark tool. A must learn module.