I am hoping to go for a cultural tour to Egypt and visit the main Ancient
sights. I'm wondering if someone could recommend a Tour company that they
have been with that would do a 1 week tour to Cairo/Giza/Luxor please?
There seems many that do this but they all look similar to me so I'd
rather go with a recommendation.

Also, does a US citizen need a visa for Egypt?

I spent the month of May there last year but I went on my own so I don't
know anything about tour companies. You need a visa though. You can get
one when you get there but it is a lot faster getting out of Cairo airport
if you got your visa in advance. There are lots of companies who will help
you get them but they'll charge about $80 US. If you live in the US see
http://www.egyptembassy.us/ to get your own. Click on Consular Services
on the left.

I hope you don't intend on going in the summer. May was already getting
pretty hot but there are fewer tourists then. Good Luck. My Egypt pictures
are at http://home.hawaii.rr.com/pat/MapLinks.htm