I agree with Colino. Haven't been to Rotterdam yet(despite all bad reviews there is a trip planned for 2013 though

). Den Hague is lovely(been there in May and November this year), lots of green spaces, the beach and a nice coffeeshop scene(definately check out Dizzy Duck and Cremers there.). Will go again.
I have been to Nijmegen a couple of times over the years(just have been about a week ago for a mini-break of some days

). Charming place, also lots of green spaces and a nice coffeeshop scene. In general the shops offer ok weed and hash(tend to have better hash). Weedwise they tend to sell no premium buds(smaller ones,leafy, not that appealing)but at very reasonable prices(you will hardly find any coffeeshop there charging more than 10€ for a gram of weed.) Hashish is also very reasonably priced(most expensive is 15€. Not saying this is cheap.).Most places(have been to all of them) are really big in comparison to Amsterdam.
If you're into hashish you have to visit Kruidentuin! Lovely place owned by a moroccan family, it's really hash heaven and one of the very best places nationwide! They offer about 10 sorts of hashish(afghan, gold maroc, huismerk, cristal, top polm(6,5€), twisla(7€/g), paki(8€), manali(8€), caramello(9€), chocolat(10€) and nougat(12,50€ if outstanding(!)15€). The stuff I remember the price I often tried and the quality is at least good. They seem to never change their menu. Weedwise they offer four strains: Shiva(7,5€), Santa Maria(8,5€), Turbo K(9€) and Haze(10€). Tried them all and they were good enough. On top of all there is a lovely house cat(female)and they do serve fresh moroccan mint tea.
I also like Kronkel for atmosphere(huge menu of beverages and soft drinks). Their menu is relatively big, too. Dakota is a great place as well. Good prices as well.
Better stay away from Dreadlock and Jetset(located same small street as Kronkel, more of take away places.). The other coffeeshops are better in my humble opinion and you can't really go wrong there..
If you're going there have fun(where ever you go) and report back if possible

!