If you can afford it, buy a speaker system with at least a dedicated center channel. Dialog is almost always mixed to the center channel in 5.1/7.1 mixes. Which means that you can just turn up the gain on the center channel speaker, while leaving everything else down. The result is magical — it's like turning down the "background music" slider in a video game :)
You don't even need to set up the surround speakers. Having a 3.1 setup has improved my enjoyment of TV and movies substantially. My understanding is most if not all receivers will downmix the surround into your L and R channels.
