If you've never gone out to the spots around Westerpark, there is a lot to be said for the 20 minute bike ride. The Culture Park Westergasfabriek is a former gasworks, and "oozes a unique mood of adventure and energy."-from the website:)
Within the park, you will find the Flex bar, Pacific Parc, and other nice locations for weekend partying. The Pacific Park also often has good Sunday afternoon DJs. Additionally, there are funky breakfast and lunch spots, and the ExpressoFabrik with fantastic cappucino freddos.

Recently I went to the cinema at the Westergasfabriek, called Bioscoop het Ketelhuis. They play an interesting selection of international independent films and afterwards, you can go on to one of the bars for a drink. When I went, however, it was a special night. Free popcorn flowed, very cheap drinks were on offer (1 euro beers) and a cool jazz band played live. I don't know if this unique event will happen again, but I always recommend going out to the park anyway. There is always something happening, and it is just far enough that you feel you've escaped the city for the day (or night).