There's a HL2 one lying around in a dead thead somewhere in this forum. There was a HL1 one made years ago too, I think. The maps end up overlapping though so it doesn't work very well.
http://www.nextdimension.org/bmrf/
Half-Life 1 Overview Map (It would have been cool to have seen this in sections, since the game goes deeper underground several times - it's practically impossible to work out what happens after the cargo elevator ride in Unforseen Conseqences.)