In contrast to Cairo's large party boats, a much more relaxing version exists, the felucca. Unlike the motor-driven party boats, the feluccas use sails and only have enough space for around 12 people. Importantly too, there's no Sha'abi music being blasted through speakers (unless you request it), instead, you can bob along the Nile and relax to the muffled sounds of the city which surrounds you. It's a great end to an exhausting day and you can even bring food along for dinner if you so wish.
Normally you rent the whole boat for the hour, and the price is pretty reasonable, especially if there's a lot of you. The feluccas are slow and you won't stray too far from where you started, but that won't matter too much as you'll be relieved to finally find some relaxation in this exhausting city.
While there are numerous places to get a felucca, I've always found the guys near the Four Seasons in Garden City to be easy to deal with, respectful, and reasonably priced. Remember to tip your captain!