Drush is probably one of the most useful tools a Drupal Developer has in his/her arsenal. Drush is a command line shell for Drupal and it can save you a lot of time when installing or updating Drupal instances with many modules.
Drupal 8 Alpha 6 is out and it has a migrate module in there! It even has a few complete migrations: variables to the configuration files owned by system module.
One of the coolest features that made it into Drupal 7 without much (if any) fanfare is the Queue API. Drupal's Queue API is a pluggable system that allows you to queue events for later processing.
Ever since we launched our site re-design, we’ve had a pretty steady flow internal change requests – add links, change fonts, re-style buttons, adjust layouts, modify permissions, etc.