StumbleUpon is a great site for finding web sites and blogs you might not otherwise come across. Of course many well known sites are there as well.
In my perusals I came across the following five mapping/GIS sites that I thought were interesting.
FlashEarth – Here is a nifty little satellite imagery viewing application. Flash Earth is refreshing because it does not look like Google Earth. Yes, it is flash based and it pulls its imagery data from Microsoft and Yahoo.
Wikimapia – Yep, it’s a Google Map powered wiki. Launched in 2006 there are over 15,000,000 places already marked. You can use the site for free and anyone can upload information without registering.
Maps Of War – Another flash based map site Maps of War is a collection of maps having to do with wars and war related subjects.
IRIS Seismic Monitor – The Incorporated Research Institutions for Seismology is a consortium of universities that aquire, manage and distribute seismological data. The Seismic Monitor is the geospatial mapping application they use for the distribution. The application is not perfect. You can only zoom to a small scale view of an area but the information is interesting. Play around with it and see what you think.