Or, just buy any have-decent cheap speakers (ideally powered), that accept input with a headphone jack.
Then you just need a cheap 3.5mm headphone jack to jack cable, from any electronics store like Radioshack.
This way, you aren't relying on a dock. When iPods stop being made (or you change to a different brand), the dock connector won't be that useful, because it's proprietary to Apple. 3.5mm jacks have been used for years and will continue to be used for years too.