WebSnapr Preview Bubble and Snap Preview Anywhere both extend links to external websites to have a popup window that shows a preview of the page being linked. This should help with letting your visitors know that it's an external link, and what's on that destination. These add to page download times, however.
Snap preview requires visiting a service provider website and registering with that service provider to get a key.
External Links "External Links is a small module used to differentiate between internal and external links. Using jQuery, it will find all external links on a page and add a small icon indicating it will take you offsite." This module simply installs and takes care of itself.
URL Class "A simple filter which adds a CSS-class to each URL according to its target. This lets you easily distinguish between internal and external URLs, and assign a unique style to each URL based on its destination." With this module you could implement something like the External Links module, but URL Class doesn't itself make any different display for external links. With URL Class you must modify your theme to detect links modified by the URL Class module, and to use CSS to make them display differently.
URL Icon Detects links to external websites, retrieves their 'favicon.cio' file (the little icon some web browsers show in the location bar) and inserts that icon next to the link. It helps make external links visible.
yahoo weather "A weather forcast displaying module. Based on the Yahoo weather API. "
Service links "The service links module enables admins to add links to a number of social bookmarking sites, blog search sites etc. Includes sites are del.icio.us, Digg, Reddit, ma.gnolia.com, Newsvine, Furl, Google, Yahoo, Technorati and IceRocket."
Avatar gallery "This module provides a block and page with a composite image of all the avatars of a site. It serves to promote a sense of community around a site..."
Avatar Selection "he Avatar Selection module allows the user to pick an avatar image from a list already loaded by an administrative user. It is also possible to disable the uploading of pictures by users and only allow them to select an avatar icon from this list."
Evoca Browser Mic "This Module allows site admins to add the Evoca Browser Mic as a block to their site and have visitors record comments right from the comfort of their browser."
MySite "MySite pages let users create a personalized summary of the site. The MySite module duplicates the functionality of tools like MyYahoo! and Google's personalized homepage."
Open Search Plugin allows your Drupal site show up as a search engine in your browser.
jQuery FontSizer Puts a couple buttons on the page letting the user increase or decrease the fontsize. Among other things, would help people with 'weak' eyesight to read your site. The documentation doesn't say how to enable the module - what it does is implement a Block containing the buttons. Simply enable the block somewhere on your site layout. Requires jQuery Cookie.
JSFX offers a set of "effects" (FX) using Javascript. The module is also simple enough to support adding other effects. The effects include making blocks and comments collapsible. Javascript Tools is like JSFX in that it provides some javascript special effects. Some of the effects are the same as in JSFX, some are different.