Ham Mapping ,
look ups by state or zip or call sign
DX Cluster online ! Real Time, Real neat !
DXCC info official from the ARRL.
Call Sign servers (Local & DX) I particularly like QRZ, its a nice collection from many sources.
ITU Prefixes right from the ITU. Great for finding the country name for those odd prefixes.
Great DX info! #CQDX IRC channel! on any of the Othernet servers.
eQSL
an online QSL service, neat for collectors but not recognized by many
awards givers (yet).