Holder.js is a library for generating image placeholders.

Its use is very simple, requiring you to add only an img tag and specify the required dimensions of the placeholder.

The placeholders can be customized quite a lot — there are three default themes, and you can add new ones –, and the plugin can be set to run only in a specific location of the website.

Pageguide.js is a jQuery plugin for creating interactive website guides.

Pageguide is a great way to introduce users to your new website layout our web app.

It’s easy to implement — with unordered lists and just a little code, you can get a guide up and running in no time.

The guides created with this plugin are unobtrusive and the user may simply close them if they’re tiring.

Knob is a jQuery plugin for creating an iPod-like interface element.

The knobs created with this plugin are easy to style. Although there isn’t a documentation, the plugin has few options and is easy to grasp from the example source.

Knob is a great way of spicing up an older design, and it’s especially useful when creating iOS apps, as iOS users are likely to be familiar with such UI elements.

Scroll Path is a plugin for creating scroll paths with a simpler markup than you’d expect.

The paths are marked on a canvas element, and the plugin supports rotation on some browsers.

Once the plugin is initialized, you can point to specific points in the path, and ease or animate to them.

Scroll Path is a very interesting plugin if you don’t mind taking the time to draw the actual scrolling paths.

PageScroller is a jQuery plugin for smooth and easy navigation.

By default the plugin provides you with four navigation types, all of which are useful in some circumstances.

For example, ‘next & prev’ navigation is quite handy for mobile phones, and so on.

PageScroller ships with several useful options and easing functions. The code and the wrapper are both dead simple; this is an excelling plugin, at least from a brief glimpse.

Tinycon is a neat little (3.6kb minified) plugin for changing the favicon of a website gracefully.

The plugin falls back to a number in title approach if the browser doesn’t support changing the favicon.

Tinycon is useful because it provides a more aesthetic way of showing application alerts–e.g., think the pretty Gmail favicon– in a non-intrusive way.