ericjuden

This plugin allows you to use $_COOKIE, $_SERVER, $_SESSION, $_GET, $_POST and $_REQUEST data in a Gravity Form through the merge tags of a field. I’ve only really tested this using a hidden field.

Gravity Forms Extended Merge Tags

It's amazing how few people seem to know about this plugin. Incredibly simple, but also really helpful when using $_SESSION variables to track website visitors.
I use it to get referring website data, so I can easily store it in a $__SESSION variable. Then when the visitor fills out a Gravity Form, I can pass along the stored vars.
I crafted a Lead Source Tracking for Salesforce script that uses this plugin to pass along the details to Salesforce when a form is submitted.



Brilliantly simple

This plugin allows you to use $_COOKIE, $_SERVER, $_SESSION, $_GET, $_POST and $_REQUEST data in a Gravity Form through the merge tags of a field.

curlybracket

This plugin creates a widget which will show the title, thumbnail and link to the last 5 posts a user has consulted. 
To store the data it uses sessions.
Session handling is provided by slightly modified functions from the simple-session-plugin by pkwooster.

Last Seen Posts Widget

Show title and links to the last 5 posts a user has consulted.

Gravity Forms Extended Merge Tags vs Last Seen Posts Widget