Ehi
@Doktor Dub, I see you already got some pretty comprehensive recommendations so I'll just add a few things. Can't help with concentrates since I've never looked for them.
On
this geocities-like website you can find some menus, not that frequently updated but just to give you an idea.
I'm absolutely in love with Amsterdam, I especially like the South and South-West parts of the city (De Pijp, Vondelpark).
For coffee shops, it really depends if you want to consume there or just buy and go elsewhere; always take into account the secondhand smoke problem
@The Beagle pointed out. Also, if it's your first time you might want to go check out one of the famous ones like Amnesia, Barney's, Green House.
I personally prefer a quiet atmosphere combined with good quality, and my favorite coffee shop is Katsu, super friendly stoner staff and average prices. Others I would recommend are 1e Hulp and Boerejongens West (Boerejongens are owned by the guys of Amsterdam Genetics, so it might be worth looking into it).
One thing I haven't had the time to do (yet!) is take a short train trip to Haarlem, apparently not touristy at all and as such great atmosphere and prices.
This is a link to a map with all the coffee shop in Amsterdam, updated last January. I think if you save it on google maps with your account you can use it on the phone while you're there, did that last time and it was pretty convenient.
There's a lot of stuff to do in Amsterdam, but the old cliché of casual wandering along the canals holds true for me. The Van Gogh museum, the Rijksmuseum and the park around are of course a must see, and the Begijnhof is a cozy oasis of tranquility suspended in time. A trip for some street food at the Albert Cuyp market is also worth the effort.
I've only been to Rotterdam once, half a day and just for buying stuff. I found an AMAZING - albeit expensive - Super Silver Haze but can't for the life of me remember the name of the coffee shop. I went and got me some Jack Herer at Sensi seeds, and some other random stuff in another walk-in coffee shop.
The city itself is nothing special imho, very modern and very Dutch (no offense!). Compared to Amsterdam, buying and consuming cannabis felt a lot more like an economic transaction than a lifestyle, if it makes sense. Ime prices are a bit on the high side, too.