Below are some mapping resources that you may find useful.
Coordinate Conversion Untility
TopoZone Topographic Maps
US Geological Survey Search
What's my Gridsquare?
Airport and Navaid Locator
Address, phone number lookup.
If you're putting up a repeater on an existing tower, you may want to look up information about the tower and what other servicesare located there. The FCC search site allows you to do that based on Call, latitude and longitude, county and state, etc.. Note this site takes some practice to learn all the "features". .
FCC Universal Licensing System
FCC Antenna Structure Registration
FCC Commercial Database Searches
RadioSoft Web Site, Propagation Modelling Software
FCC HAAT Calculator
Distance Between Two Points
Lat/Long for a known point, distance and azimuth