Literally got back from a driving trip to Amstedam yesterday.
There are a fair few new buds around since I went last year, such as the 100% pure sativa Dr Grinspoon in Barney's, but at 17 it's a little expensive. Thankfully Dampkring now do Kali Mist too, as the Grasshopper used to be the only place, which is full of noisy Americans and charges 22/g.
Definitely ask the locals where to go if you want the real shit. I popped into the Sensi Seed Bank, who have unfortunately closed their coffeeshop as I was dying to try Ed Rosenthal's Super Bud, and the girl in there told me the best places to visit.
If you want a little more than bud you can always buy some shrooms in a shop then rent bikes and have mini-adventures around the city. As people have said it's absolutely beautiful and definitely worth exploring.
The locals are friendly as long as you don't act like a blatant tourist, but it's the bikes and trams that are much more likely to do you damage than the people!
I've used this map of the coffeeshops every time I've been and not got lost once:
http://www.coffeeshop.freeuk.com/Map.html