1. Anne Frank House - yes yes yes! An absolute must! I believe you can buy tickets before hand online. I waited in line since I went with a school group and wasn't sure when we'd be done so that I could see this, and we waiting in like for about 30-45 mins once we got there at 5:30. Be prepared to cry, it's very sad to see, but amazing at the same time.
2. Canal Cruise: would love a dinner cruise and am looking for recs! I did one through my school group and it was fun, I'd say it was worth it. I saw a lot of architecture that I would of otherwise missed. We went on a morning cruise, so I have no recs for a nighttime/dinner one, sorry!
3. The Nine Streets: worth it? -didn't go/see it
4. Rembrandt Museum: worth it? That's the rijksmuseum right? I'd skip it. They were undergoing massive renovations this summer and a lot of the exhibits were closed. Then again, I've seen Vermeer in DC years ago, so I wasn't disappointed. I'd go to the Van Gogh museum, which I heard was much better, instead.
5. Red Light District: safe at night without a tour guide? - I found it to be safe enough. We went around 8 or 9 pm. All I heard was beware of pickpocketers, but I had no problems. It's exactly as how I thought it would be, and I was rather entertained by it, since it's clearly mostly foreigners who are there and are gawking lol.
6. Willet Holthuysen Museum: any reviews? Didn't go
7. Amsterdam Dungeon and Madame Tussauds: reviews? Also didn't go.
I'd also skip the Sex Museum, it was really boring, and was mostly nude photos or mannequins in either sexually posed positions or just placed to look provocative. It wasn't expensive, about 4 euro, but it was a waste of time and money IMO. I went to the Heineken experience while I was there also, which was ok. The people that drank beer really enjoyed it, but I'm not much of a huge drinker to begin with, and I found it to be rather boring. I think the best part about Amsterdam was the canals, architecture and the Anne Frank Museum to be honest, and I think 2 days is enough time to see everything that you want to. Have fun!