I found the well-known pyramids to be rather disappointing given that they are on the edge of what many might consider a slum. However this was at the end of the 80's so things may have changed for the better (or worse....).

I did really enjoy the pyramids at Sakkara which are also not that far outside Cairo and where there seemed to be less people (both tourists and people trying to hassle you for money). I can certainly recommend a trip to Sakkara. Here's a link to some more info:

Sakkara