@MD: exactly. I wish I had 2 weeks to spend! But my vacations come in tiny slices, maybe 6 days at most, and we try and cram as much into that time as possible.

Unfortunate if your vacation is short, especially from North America, since it's a day each way. Typically you arrive in the afternoon, and do nothing until the next day. We left Canada mid-Friday, arrived 3PM Saturday in Cairo, and did not start touring until the next morning. We left Cairo about 9AM, short stop in Franfurt, and I suppose we could have gotten all the way home by 11PM the same day if the Frequent Flyer seats had been available, but flew home 6AM the next morning, just a little late for work in the end.

My "top items" then would be - in order -
-Giza, Cairo museum.
-Step pyramid at Sakkara if you can fit it in. Tomb of Ka-Gmni was amazing, for 4500 year old reliefs.
-Valley of the Kings. (Luxor and Karnak Temples)
-If you can fit it in, Abu Simbel.

Additional things to see in a short visit:
-old Cairo, or Coptic Cairo, if that intersts you.
-if timing is right, continue on from Sakkara to Darshur to see the Red Pyramid, Bent Pyramid. You can climb inside the Red Pyramid.
-If you like the temples, there is the Ramsseseum and Temple of Ramses on the Luxor west bank; plus Hapshepsut's temple, and tombs of some nobles; village (and some tombs) of the workers - all right across from Luxor so there's a lot in the area to keep you busy. Luxor Temple, Karnak, and possibly Luxor Museum are open late if you are the over-energetic, heat-doesnt-bother-me type.

Usually, you are done by 5PM and attractions are closing, but if you can do something in the evening, great. Alternatively, travel in the evening; however, we left Cairo at 7AM, flew to Abu Simbel by 10:30AM (1 hr stop in Aswan) then flew out at 12:20PM. (In our case, to Aswan).

If you do need tight connections, that is where an organizer on the ground can be very useful. Private guide and transport is great for the tourist sites, since you can adjust your schedule according to what you are most interested in.

So yes you can do a lot in a few days with good planning.