Just back from a couple of nights with friends in the glorious Amsterdam sunshine and we were lucky enough to stay on the Houseboat Saturnus.
The boat was clean, tidy and in great order, moored just across the water from a great pub (Cafe De Sluyswacht - also recommended!) not far from the centre (10-15 minutes walk).
Portholes aside, it was hard to believe that you were on a boat with no perceivable motion from the water, comfortable beds, perfect electrics and a great shower & toilet....the boat even had wifi! If/when I return to Amsterdam I shall definitely look to stay on the boat again.
The owner was a friendly guy too. He checked in on us to make sure we were OK and seemed very eager to make sure our stay was a good one.
Book it, you won't regret it!