50 MHz DX Maps Tip: Check "Only DX-Cluster"
N3TUQ 6m DX Map
MUF DX Map
APRS Map   May indicate possible DX opportunities on 144 MHz.
Pingjockey   This is the go-to chat page for real-time scheduling of meteor scatter and EME QSOs.
WSPR Map   There are WSPR propagation beacons on both 50 and 144 MHz.
ON4KST Chat (Region 2)   Must register to post.  This is the center of activity when an Es opening is anticipated on 144 MHz.  
Beam Spinners   Regional chatroom that was very active during 2016 January VHF contest.
JT65 Terrestrial Spots   Real-time skimmer for JT65 QSOs on 50 MHz.  Great place to find digital DX.
144 MHz Propagation Logger   Largely displaced by the ON4KST logger, but there is still some activity.
Real time map using data from the DX clusters.
DX Summit spotting site.