General
Google street view can occasionally settle disputes about how roads are named (Copying google maps to Waze is probably illegal)
http://gis.deat.gov.za/Default.asp have some GIS data
Provincial goverment site offline currently...
Freeways
SANRAL / i-traffic - have a limited amount of info
Engineering news - have strories about GFIP milestones, often with images of interchanges
By metro municipality
All seem to have a publically accessible GIS. Most have seperate maps that might be easier to work with in some cases
Tshwane
Maps site: (To be considered authoritive on suburb names/borders / street names)
http://www.tshwane.gov.za/streetmaps.cfm
The street guide work well once you figured out how to zoom in (read the instructions page)
GIS seem out of date in many cases
Johannesburg
http://www.joburg.org.za/city_maps
Ekurhuleni
Maps site:
http://gis.ekurhuleni.gov.za/