Here's to a simple dumbbell exercise that works the forearms and the biceps: the reverse dumbbell curl!
Reverse Dumbbell Curls
Not to mention there are those who don't have a barbell.
One After Another?
In the video I demonstrated doing both sides at the same time, but you can of course also go for left-right-left-right etc. It's in fact preferrable when you want to put your full concentration on the weaker side that needs to catch up.