Here are some examples of using Drupal's states API. It shows the use of OR and XOR (which only work with jQuery 1.8 or above, apparently). More examples can be found in the examples project in the form example module.

"Panels are great, but how do I change this one page?"

In a hurry to get this information up... Sorry for any typos :)

"The RealName module allows the administrator to choose fields from the user profile that will be used to add a "real name" element (method) to a user object. Hook_user is used to automatically add this to any user object that is loaded. It will also optionally set all nodes and comments to show this name."

This module lets you take the input from a field and allows using HTML and token replacement (or alternately PHP) for display.

This is the module that is used on this site for code highlighting.

I just read a great article on this that breaks things down very well. You can find the original article here: http://fredparke.com/blog/create-your-own-tokens-drupal-7

Basically, you need to use two hooks. The first one tells the system about your token. The second one contains the specific logic for your token.

"Pathologic is an input filter which can correct paths in links and images in your Drupal content in situations which would otherwise cause them to “break;” for example, if the URL of the site changes, or the content was moved to a different server. Pathologic can also solve the problem of missing images and broken links in your site’s RSS feeds."

A nice way to add placeholders to input fields. "This module auto-converts form input fields with space-hogging labels into compact mobile-friendly input fields, with placeholders that animate into much smaller labels the moment text is keyed in. "

The gist: "This module extends the functionality of the core 'file' field, adding new capabilities to the file upload widget, and providing a new extendible field formatter for displaying lists of files."