Beware the audiophiles in this thread; Flatpanel TV speakers are shockingly
bad and even cheap HT-in-a-box solutions are orders of magnitude better than them. My advice would be to go for something cheap if you're not going to go all-out.
All you really need to make a big difference is a subwoofer, in most cases but I found that the HTIB packages with a Dolby certification at least guarantee a minimum sound quality. It's nothing great, but it eliminates the utter junk from your selection.
Something like this
wouldn't be a bad idea - you also get HDMI-CEC and I've used a similar system to upmix stereo to pseudo-surround with satisfying effects.
No, it's not the last word in audio quality.
No, the frequency response might be lacking in a few places that muddies complex bass riffs or emphasises low-bitrate MP3's
Yes, the damn thing just works over HDMI-CEC so I don't have to juggle remotes and keep switching input devices all over the place.
Yes, the sound is several times better than the TV's speakers.
Good enough that I don't really notice anymore, and good enough that just occasionally I am surprised by the sound quality for what is a taboo topic among audiophiles: cheap HTIB packages.