http/www.logitech.com/en-us/product/speaker-system-z623?crid=1589
There are many choices for computer speakers, depending on your budget, any space constraints, and what you wish to listen to.
I linked to a 2.1 system, which has left and right speakers, as well as a subwoofer. This is good for general purpose listening, as well as music. For gaming, and movies, a 5.1 speaker system is another good option. If you do not have the space on the floor for a subwoofer, than a 2 speaker system can be used.