To get to the pyramids from Cairo, you have several options. The most "luxurious" option would be to take the No 355/357 bus, which provides air-conditioned travel to the pyramids in a big white bus. The bus runs every 20 minutes, with service from Heliopolis to Giza. The most convenient "stop" is located behind the Egyptian Museum -- where a number of tourists gather to get on the bus (even so, you may still need to flag down the bus as the stop itself is unofficial.) Bus fare is E£2.

There is also microbus service from Cairo to Giza. Microbuses leave from a spot near to the Hamses Hilton hotel. Fare for a microbus is 25 pt. If you just can't get a handle on the bus schedule, then you'll probably want to take a taxi to Giza.