ARRL -- excellent resource for many different topics
QRZ -- look up licenses and station information
AA9PW - Amateur Radio Exam Practice
FCC Database Search of amateur radio licenses
AE9Q - What call signs are available?
NOAA Space Weather Predictions
Voice of America Propagation Forecast Tool
eQSL - confirming contacts on the air
LOTW - ARRL Logbook Of The World
Ping Jockey - meteor scatter chat room
Array Solutions - surge and lightning protection
Digikey - electronics components
DX Engineering - retail outlet with a wide selection
Dyneema Cord - excellent choice to support portable masts
Ham Radio Outlet - retail outlet with a wide selection
LNR Precision - ultra-lightweight CW transceivers
McMaster-Carr -- every piece of HW you will ever need
Max Gain Systems - fiberglass push-up masts
MFJ - retail outlet with a wide selection
QTH - ham radio classified ads
QRP Guys - collection of QRP gear
QRP Labs - colletion of QRP gear
Universal Radio - retail outlet with a wide selection
APRS tracking map (also on iOS)
WB8NUT - brief overview of various digital modes
WSJT-X suite of weak-signal software
FLDIGI software - does nearly everything digital (except WSJT weak-signal modes)
Robot36 - SSTV decoder for Android
APRSDroid - use APRS service from your phone
Repeater Book - listing of repeaters (also on iOS, Android)
Echolink - connect with repeaters using your smartphone (also on iOS, Android)
AMSAT - national organization of satellite enthusiasts
DK3WN comprehensive satellite resource
"ISS Detector" - great tracking app for all amateur satellites (not just ISS)