General GIS Information
Directions Magazine — Online magazine for GIS and related technologies.
ESRI ArcUser Online — Magazine for users of ESRI software; good place to look for inspiration for a research topic.
ESRI Virtual Campus — ESRI training and education; good if you need to learn a new GIS skill.
GIS Lounge — Information for GIS professionals.
Cartography, Design, and Visualization
Color Brewer — Interactive tool for selecting map color schemes.
ESRI Map Book Gallery — Examples of attractive maps made with ESRI GIS software.
Flowing Data — Statistical data visualizations.
Library of Congress Panoramic Maps Collection — Historical bird's-eye view maps of US cities.
Georeferencing (datums, coordinate systems, projections)
GPS.gov — Everything you need to know about the Global Positioning System
Interactive album of map projections — From Penn State University.
Interactive map projections — From a Brazilian researcher.
Matching the Map Projection to the Need (ACSM) — Expert report on map projections
Mean Sea Level, GPS, and the Geoid — From ArcUser Online
The Impossible Map — Old educational film that really shows how map projections work
Township, Range, and Section FinderConversion tool: US Public Land Survey System to latitude/longitude