Here's a list of my favorite map sites:
http://maps.google.com/ (Google Maps Beta)
Excellent site with both roadway and satellite maps. Has a clean interface (that works w/ firefox), and the drag/panning feature is the best I've found. The maps load very quickly, but the resolution can be poor depending on where you're looking.
http://terraserver.microsoft.com/default.aspx (Terraserver USA)
Good site, has topographical and B&W satelite maps.
http://www.topozone.com/ (Topozone)
Strictly a topo site, but the maps are better quality.
http://www1.nysgis.state.ny.us/MainMap.cfm (NYS Interactive Mapping Gateway)
Good site if you live in NYS, and are an IE user
. It has roadway and color satellite maps, but I don't like the interface and loading time.
I also play around with a program called Microsoft Streets and Trips. Its helpful when planning routes and stuff like that, but it misses a lot of the smaller bodies of water around me.
Please share any sites or software you guys know of, I'm a mappin fiend.