For decent quality sound I take the line-level audio out from the Pi to my Sony surround system. (I don't actually like Sony equipment, I've had lots of bad experiences with it, but it was a gift).
For basic audio I use a cheap PAM8403 stereo amp module. I drive it from the same 5V supply as the Pi, which gives a small amount of hum when it is idle. It is only driving a small speaker for my doorbell, but it is adequate for that and we can hear it anywhere in the house. The module does require some soldering. Although it is stereo it won't be damaged if you only connect one speaker.
Others may advise better options.