The taxonomy system in Drupal is great base for many features. Here are two modules which extend the core functionality in fine way.
Use the smart_trim module. It provides a couple of trimming options for the formatter of textfields (text, text_long, and text_with_summary).
Profile2 is a nice module to build user profiles. However it lacks some basic functionality. This modules tries to fill this gap.
There is a nasty bug in Pathauto module, which causes troubles when you use Views Bulk Operations module (or generally when you save a node programatically).
Today I ran into an issue where a form was not submitted correctly. The form was on each row of a views page, and the view was cached using cache_actions module (which provides a cache which can only be cleared via a custom rule [from the rules module]).
Date field is fine if you want to set a definte date, for other use cases, when for example the definite year or month is irrelevant you might need another field for that. Here are some options, I have found:
http://drupal.org/project/double_field - two textfields (in one) with different widgets - eg text for amount and dropdown for unit.
Using the flag module, people can maintain lists of nodes on a Drupal site. To access their list of bookmarks, a tab on the users page can be provided. This tab is accessible at user/[uid]/bookmarks lets say.
For the Entity Reference (http://drupal.org/project/entityreference) there exist two modules, which make it possible to create the nodes you want to reference on the fly. Those are
With Views module you can create pages and add menu items to them. The ugly thing is: once you have created a menu item via Views, you can not get rid of it, because even if you remove it in the Views interface, its corresponding row in the database still hangs around.
Here are some short notes about interesting module I recently discovered. All the listed module are available for Drupal 7 already. I have to admit, that I had no time to try them so far.
Recently a module by eaton catched my attention: Entity Views Attachement (EVA). As I have been using Viewfield quite often I was wondering, what the actual difference between those two modules is.
Wolfgang Ziegler aka fago did a session