Here are some of my favorites that I don't see anyone else referring to:
SmallMenuPlus is a great tool for making the main menu much more flexible - and more like the Start menu on a PC with submenues. VERY customizable.
http://tillanosoft.com
TodayAgenda is a nice little tool to make the display of the Outlook Calendar more flexible on the Today screen - several days, collapsable, font sizes etc. etc. also VERY customizable.
http://tiews.info/index.php?show=&lang=en
ListPro is a list program (Surprise!) that is suberp for people with bad memory (like me).
http://www.iliumsoft.com/site/lp/listpro.php