Unc has the right of it. The nunchuck may come with it anyway, mine did. I would also recommend a charging unit for the handsets as this will save on batteries in the long run.
You may surprise yourself Snoops the Wii is a very 'social' bit of kit.
Just a word of warning on the charging kits - they are known to screw up the controllers. This has happened to both mine and a friend who bought a different model.
Resulting in having to purchase another bloody controller at the energy saving price of £29.99
Apart from that even I could set it up....
Another thing you may need is a memory card but don't buy the Wii version as they are a rip off and it will work with any make of SD card.