Extensions & Software
SpatialEcology.com: Website of Hawthorne Bayer, creator of Hawth's Tools (legacy) and the new Geospatial Modeling Environment. If you are using GIS in wildlife research, then you will want to use this (and thank Hawthorne)! FREE.
DNRGPS Application: The single best piece of software for sharing data between GPS units and GIS software. Make shapefiles or Google Earth kml files on your desktop and upload them to your GPS; or, download your track and waypoints as shapefiles (or kml) for easy viewing in GIS/Google Earth. FREE, open source software courtesy of the Minnesota DNR.
CorridorDesign.org: A nice collection of tools for use with ESRI's ArcGIS, including an ArcGIS Toolbox that can be used with model builder. If you were a fan of the old topographic position index by Jenness Enterprises in ArcView 3, then you'll be happy to know that this functionality is available in Corridor Designer. Manual and tools give a nice step-by-step overview for creating habitat suitability index and corridors. There is also a nice page of descriptions and links to other GIS tools. FREE.
Jenness Enterprises: Website of Jeff Jenness, wildlife biologist and GIS consultant. Jeff has created several ArcView 3.x extensions, as well as a handful of ArcGIS 9.x and 10.0 tools. A favorite among these is the Mahlanobis Distance Statistic tool for habitat suitability analysis. FREE.
ET Geowizards: A collection of tools that includes a lot of things you can't understand why ESRI failed to include in their overpriced software. FREE. (Paid version has no restrictions.)
Easy Calculate: So you want to quickly calculate something in the ArcGIS field calculator without having to write the code? There's a good chance you can find the code already written for you in Easy Calculate. FREE. (Paid version has no restrictions.)
Ohio Statewide Imagery Program: High resolution (1 ft. or 6 in.), leaf-off, aerial photos of the entire state in MrSid format. Includes both RGB and CIR. Also, high resolution DEMs (2.5 ft.) and LIDAR data available. Simply fantastic. If you want to really appreciate this resource, work on a project in a state without such data (e.g., Michigan). FREE.
Ohio DNR Geographic Information Management System (GIMS): Data from the Ohio Department of Natural Resources.
National Wetland Inventory (NWI): Updated NWI data for Ohio, Indiana, and Illinois being produced by Ducks Unlimited for the US Fish and Wildlife Service.
Multi-Resolution Land Characteristics Consortium (MRLC): The easiest place to find and download the National Land Cover Database (NLCD) showing land-use/land-cover (LULC) for the entire US, as well as several derived data layers (e.g., canopy cover).
Cropland Data Layer: From the National Agricultural Statistics Service. Agriculture and grasslands seem to be the most commonly mis-classified LULC categories, especially in the NLCD. This layer is the best I have found for identifying agricultural areas. Data is available from 1997 - present.
The National Map: Data from the USGS.
Earth Explorer: Data from the USGS.
Other GIS Resources
ArcGIS Forum: When all else fails, turn to the forum to ask your GIS question or vent your frustrations about ESRI software. Sometimes it's useful to check out the old forum, too.