For me there are two major sources:
a) beacon monitoring stations
b) reverse beacon network
There are 2 beacon monitoring stations close to me. Unfortunately one got hit by lightning and other guy is moving to new qth.
So - they are both down at the moment. Fortunately there is a monitoring station
http://www.k0koc.com/faros/chrome.asp in Maryland and I check how it copies OH2 beacon which is close to me.
RBN (reverse beacon network) is another cool thing. I send my cw "cq" for a minute and after that I have very good overview how I'm heard on the "other side".
http://www.reversebeacon.net/dxsd1/dxsd1.php?f=0&c=es1tu&t=dxUnfortunately their telnet server at telnet.reversebeacon.net:7000 has been a bit unstable lately, but I hope it will be fixed soon.