Warning: The buildamodule.com links below refer to a paid-for tutorial resource giving limited access for free (however the videos referenced below are free).
Who says forms can't be fun? This collection of videos from BuildAModule starts takes you through building a simple form in Drupal 7 and adding interactive elements like autocomplete inputs, Ajax-loaded fields and instantaneous form manipulation with the #states attribute.
- YouTube Video: How to Build Beautiful Forms in Drupal 7
- Drupal 6 Form API Quickstart Guide
- Drupal 7 Creating a "builder" function to generate a form