Well I use ArcMap on daily basis to aid the masterplanning work we’re doing, one thing I’ve found difficult is producing paper maps! Sure you can place all your data in one file but making it in to a map that other people can read is hard work. The one tool I recommend above all others is ArcMapBook (or DS Mapbook) it allows you to place a grid over exisitng data and make a series of paper maps to cover a city or a road network!

So it is with this in mind that I suggest you the following free tools, this list will expand some come back again if it’s not very long!
ArcMapBook: http://arcmapbook.googlepages.com/

BookMarkManager 1.4.1 Mapbook generator (website link too long for this post!)
Et Geowizards: http://www.ian-ko.com/
HawthTools: http://www.spatialecology.com/htools/index.php
ArcSketch: http://www.esri.com/software/arcgis/extensions/arcsketch/index.html
ArcSketch is great for quickly drawing out features with the correct symbology, I’ve only just started to use it and it’s great!