Here is a list of some cool Drupal 6 modules I have found. I will keep updating this list as I find more. Enjoy!

Toolbar - A Drupal 7 styled configurable toolbar for Drupal 6, currently Beta 2, but works well:

http://drupal.org/project/toolbar

Avatar Blocks - Replace Drupal's Who's online?, Who's new? and Buddylist blocks with ones that display the users avatar. Easy to configure and you can customize it via CSS.

This link downloads the Drupal 6 version in zip format.
http://drupal.org/files/issues/avatar_blocks.zip

Tab Tamer - This handy module allows you to hide tabs displayed on the user Tab Menu. great if the current list of tabs display more tabs than you prefer.

http://drupal.org/project/tabtamer

QTChat - Facebook style chatbar. This module is currently in development and also requires the QTChat Views module. Looks promising...

http://drupal.org/project/qtc
http://drupal.org/project/qtc_views

File Depot - The filedepot module is full featured Document Management module that has a google docs like feel. It fulfills the need for an integrated file management module supporting role and user based security.

http://drupal.org/project/filedepot

Home Box - Home box allows your users to have a page that behave the same way as iGoogle, Netvibes or BBC.co.uk. (Requires the JQuery UI module and JQuery library.)

http://drupal.org/project/homebox
http://drupal.org/project/jquery_ui
http://jqueryui.com/download

User Plus -The userplus module enhances Drupal's user administration and Organic Groups' subscription administration by allowing administrators to add multiple users at once, make multiple group assignments at once, and make multiple user role assignments at once.

http://drupal.org/project/userplus

Module Filter - This very handy module reorganizes the admin/modules list into sections. It adds a menu to the left of the modules list and allows you select the module section, rather than displaying a long list of modules. If you have lots of modules installed, you will find this module indispensable.

http://drupal.org/project/module_filter

That's it for now, but I will keep updating the list with new modules as time permits. All the best, Shane.