Useful under-the-radar Drupal modules
pngFix Module
This module includes the jQuery pngFix plugin, which uses the Twin Helix method of providing PNG transparency support to the IE 6 browser. The module provides an administrative interface where you provide a list of jQuery selectors to target for pngFix.
Automatic Nodetitles Module
Automatic Nodetitles provides the ability to automatically set the title for nodes using tokens. Think of it as pathauto for titles. You also get the ability to hide the node title textfield on the node create page. This module is highly usable in situations where you have a content type that doesn't make sense to have a user manually type a title for each node.
SpamSpan Module
SpamSpan provides a new input filter that obfuscates email addresses in an effort to hide them from email harvesters using the SpamSpan method. I haven't had enough experience with this module to know how well it blocks harvesters, but as a filter, it's super easy to use. Just enable the filter and forget about it. It even has a nice way of degrading when JavaScript is not used.
Path Filter Module
Path Filter provides a new input filter that replaces relative paths with absolute paths at the filter level instead of at the input level, which is TinyMCE's method. This is an essential module if you ever move your Drupal site from one path to another (www.example.com/dev to www.example.com). This module requires a bit of hacking if you want it to work with TinyMCE. I have a patch for this issue here.
LoginToboggan Module
LoginToboggan provides several extremely useful utilities to customize the user login process. The most useful abilities allow users to login with an email address or username as opposed to only a username and to redirect a user to a page after registration. The latter is very useful for conversion tracking with a system like Google Analytics.
