VFR sectionals:
https://aviationtoolbox.org/members/...s/map_explorer
http://www.fboweb.com/antest/ge/intro.aspx. See the
US Sectional Charts link. The thing uses Google Earth but sadly they are not updated. Otherwise, incredible stuff.
Also useful:
http://www.myafd.com/
http://www.naco.faa.gov/index.asp?xm...hart_bulletins
As far as free online IFR enroute charts are concerned, the site
Bo Nalls pointed out is the best I have known