used...
Anthony Gallo Micro TI or Nucleus off ebay. I can't believe they go for $50-$70. They're usually $200+ new.
They're perfect for surround since they're small and can be placed where they need to be without bothering the wife (or future wife) too much. Their mid-range is very good, just don't expect any extended highs or lows. It's a single speaker, but one of the better ones.
I also tried the Boston Acoustics SoundWare. It's not as even sounding as the AG's but it's great for surround.
Other tiny surround speakers I suggest used:
Orb Audio (AG Micro TI, Nucleus) identical clone
Mirage NanoSat
Morel SoundSpot ($80 new off ebay)
With smaller surrounds, you'll want to reflect the sound against the wall to disperse it. If not you can place a some type of decoration that isn't flat in front of it.