This is not intended to be a fancy exhaustive list. But I have these set as bookmarks in my browser and I use them all quite often. You may find them useful.
DX Summit (DX spotting resource particularly useful for searching spots to correct calls you may have logged incorrectly)
DX Heat (DX spotting resource that displays a "heat map" showing you where all the action is)
DX Watch (Web-based DX spotting network)
DX World (Stories and news related to DXing)
DXScape (Web-base DX cluster)
The Daily DX (Subscription news site for DX run by Bernie, W3UR)
Club Log (Popular web-based logging platform with OQRS for QSLing)
DX News (News related to DX and ham radio topics)
LOTW (Online electronic QSL system operated by the ARRL)
eQSL (Online electronic QSL system)
QRZ (Online callsign lookup and logging system)