ArcGIS Tools & Extensions

Brava! DWG Viewer
http://www.bravaviewer.com/viewers.htm
A free tool for viewing and measuring DWG, DXF, and DWF files.

DS Map Book
ESRI Developer Network link
"This Developer Sample code is designed to allow for the creation of Map Books. A page is created in the book based on each feature in a grid/index layer specified by the user. Index layers must contain polygon features with a string field containing the name of each tile/page. The features in the index layer do not have to be of any particular size or shape, nor do they need to be continuous or non-overlapping. Several commands are included for generating index layers based on a uniform grid or based on selected, continuous line features"

Edit Tools
http://www.ian-ko.com/
A reference for tools (ET GeoWizard, free calculators, etc.) and resources.

SmartExporter
http://arcscripts.esri.com/details.asp?dbid=14823
Export your layout/map to DXF with this export filter created for ArcMap 9.1/9.2!

TerraServer Download Tool
http://arcscripts.esri.com/details.asp?dbid=14816
This is a valuable tool! Once installed, it makes a new toolbar available in ArcMap. With the toolbar open, click the TerraServer button and it will download imagery hosted by TerraServer (http://terraserver.microsoft.com) directly into ArcMap. This is a great way to acquire aerial imagery for an area, or simply get a better idea of where your data is located.

XTools Pro
http://www.xtoolspro.com/
A great extension for geoprocessing. With this you can do some things that would otherwise only be available at the ArcEditor or ArcInfo license level. It is priced at less than $200. Check to see if your company already has it available for you to use.