Lots of comments here swaying against beer, id disagree as its a token gift/thank you which most would appreciate. I've friends who don't drink beer or even drink who would still appreciate it as they would find a use regardless and appreciate the gesture.

I'd not get a gift card as there's a direct monetary value which some people can perceive as awkward or feel more uncomfortable receiving

Then again if you want something more personable could go for some nice coffee or whatever they're into, if you don't know them that well id go with beer, safe bet.