Live Cafe Gorissen: Those who want to go for a beer...
Brunssum doesn't have much to offer for nightlife, but this bar is pretty neat. They often have live bands playing here, mainly in the weekend (not in summer, but they do have a terrace open).
At day the bar is a place where you can eat something and sit on the terrace (in summer). In the evenings the party starts and you get your nightlife spot. Best days for nightlife are fridays and saturdays.
Koempelclub: If you want to do a nightclub in Brunssum...
Really, I shouldn't recommend this place to you.. so let me start telling that the main spot for nightlife in Brunssum is called "Heerlen", the nearest city. There is no good night transport by bus though, so you may have to face this place.
The Koempelclub (Koempel is dialect for Miner) is the only local nightclub, it mainly attracts a very young audience (the older ones head for Heerlen). There are several area's, best nights are fridays and saturdays.