This module is basically an advanced devel generate (see the devel module). Gives more control over the dummy content that gets generated by devel. (I haven't used it yet but it seems promising.)
Pretty sweet module. Easily build form based pages. It can have system variables for fields if the Variable module is installed. The forms are exportable. Uses the Form Builder module.
Really rad developer module. Use this in addition to Devel to become super awesome. One thing I like about it is the ability to clear any cache you want; you can clear the cache from just one view, for example.
Developing with Apache Solr? Then you pretty much gotta have this installed. It will show you the entire Drupal Solr entity in a subtab next to the normal devel subtabs.