The goal here is to have a list of links to help with propagation or digital mode questions. If you have any to add, please let me know.
This site draws on several sources to provide an overview of current propagation conditions.
A powerful propagation prediction tool. You can use it to view current conditions between locations. In addition, it can provide a list of the best frequencies to use throughout the day for that path.
WinLink Live Information provides you with a view into the nodes on the system
WSPR is designed to view propagation. Set your station to transmit WSPR and then see what stations can pick you up, using low power (around 5 watts).
APRS can be used for many text functions. You can use this page to see weather stations, track people who have their APRS set to that, find messages, and find WinLink Gateways and IGate receivers.