Alberta GeoDiscover = wow.

I'm probably coming across this long after everyone else is well aware of it, but Alberta Gov's GeoDiscover site....pretty amazing.
Uses ESRI's Community Maps as one of the base maps, and seems to combine a data catalogue with data viewer.   Pretty slick and expansive...
Add map services, shapefiles, csvs...
http://maps.srd.alberta.ca/GDA_Viewer/Viewer.ashx?Viewer=GDA
Steve